* Decouple AuthenticationEngine and BackendConnection

* Decouple AuthenticationEngine and BackendConnection

* Unify userName to username

* Refactor CommandExecutorTask

* Refactor MySQLComQueryPacketExecutor.isQueryResponse

* Refactor MySQLComStmtExecuteExecutor.isQueryResponse

* Refactor PostgreSQLComBindExecutor.isQueryResponse

* Refactor PostgreSQLComQueryExecutor.isQueryResponse

* For code inspection

* For code inspection

* For code inspection

* Fix checkstyle

* Rename AbstractShardingJDBCDatabaseAndTableTest to AbstractShardingSphereDataSourceForShardingTest

* Rename AbstractShadowJDBCDatabaseAndTableTest to AbstractShardingSphereDataSourceForShadowTest

* Rename AbstractMasterSlaveJDBCTest to AbstractShardingSphereDataSourceForMasterSlaveTest

* Rename AbstractEncryptJDBCDatabaseAndTableTest to AbstractShardingSphereDataSourceForEncryptTest

* Rename ShardingProxyContext to ShardingSphereProxyContext

* Rename sharding-proxy to shardingsphere-proxy

* rename org.apache.shardingsphere.shardingproxy to org.apache.shardingsphere.proxy

* Rename shardingsphere-underlying to shardingsphere-infra

* Rename shardingsphere-infra's subprojects

* Rename shardingsphere-infra's subprojects

* rename package from org.apache.shardingsphere.underlying.common to org.apache.shardingsphere.infra

* rename package from org.apache.shardingsphere.underlying.executor to org.apache.shardingsphere.infra.executor

* rename package from org.apache.shardingsphere.underlying.merge to org.apache.shardingsphere.infra.merge

* rename package from org.apache.shardingsphere.underlying.route to org.apache.shardingsphere.infra.route

* rename package from org.apache.shardingsphere.underlying.rewrite to org.apache.shardingsphere.infra.rewrite

* rename shardingsphere-database-protocol to shardingsphere-db-protocol

* rename package org.apache.shardingsphere.database to org.apache.shardingsphere.db

* move Authentication to shardingsphere-common

* move master slave rule test cases to master-slave-core-common

* move auth to shardingsphere-common

* unify package name of encrypt-core-api

* unify package name of sharding-core-api

* unify package name of sharding-core-common

* calculate lower 2 bytes and upper 2 bytes according to mysql protocol

* support mysql8 for sharding-proxy

* fix unit test

* implement AUTHENTICATION_METHOD_MISMATCH of mysql for mysql

* fix bad db error.

* add unit test

* move sharding-proxy-transport to shardingsphere-database-protocol

* rename sharding-proxy-transport to shardingsphere-database-protocol for maven module

* rename org.apache.shardingsphere.shardingproxy.transport to org.apache.shardingsphere.database.protocol

* remove transaction dependency for proxy-transport

* remove sharding-proxy-common dependency for sharding-proxy-transport-postgresql

* remove netty dependency for sharding-proxy-transport-postgresql & sharding-proxy-transport-mysql

* move SQLErrorCode from sharding-proxy-common to sharding-proxy-transport-core module

* fix javadoc

* for code style

* move MySQLAuthenticationHandler from sharding-proxy-transport-mysql to sharding-proxy-frontend-mysql

* for code style

* remove sharding-proxy-common dependency from sharding-proxy-transport-mysql

* remove dependency from shardingsphere-common

* remove dependency from shardingsphere-common

* upgrade java version from 7 to 8

* upgrade lambda expr for java8

* use java8 Optional instead of guava Optional

* use java8 Optional instead of guava Optional

* 
1. modify MySQLAuthenticationHandler's login method to return Optional<ProxyUser>.
2. check response41 database with ProxyUser's database.
3. add UT.

* resolve conflicts.

* try CI check again.

* 
1. move schema judgement to MySQLAuthenticationHandler.
2. modify UT.

* 
1. modify the input parameter of MySQLAuthenticationHandler.login().
2. modify UT.

* try CI check again.

* 
1. add ER_DBACCESS_DENIED_ERROR in MySQLServerErrorCode.
2. modify the result of MySQLAuthenticationHandler.login() to Optional<MySQLServerErrorCode>.
3. modify UT classes.

* rename to UserChangedListenerTest

* use AuthenticationChangedListenerTest

* use UserYamlSwapperTest

* modify authentication

* Authentication changed event

* Authentication changed listener

* modify AUTHENTICATION_YAML

* check style

* check style

* modify swap()

* add AuthenticationYamlSwapperTest.java

* use Authentication()

* modify AUTHENTICATION_YAML

* Authentication engine for MySQL.

* login()

* Authentication engine

* modify unit cases in MySQLAuthenticationHandlerTest.java

* setAuthentication()

* use Authentication

* modify javadoc

* modify javadoc

* modify loadServerConfiguration()

* use authentication in loadServerConfiguration

* modify unit cases

* add user

* add UserYamlSwapper

* modify YamlAuthentication

* use YamlUser

* delete new YamlAuthentication()

* add YamlUser.java

* modify AUTHENTICATION_YAML content

* use Collections

* use Collections

* modify config

* use Collections

* modify unit cases

* prefer to use Collections

* modify swap()

* add isAuthorizedSchema()

* isAuthorizedSchema()

* add userName

* modify assertMarshal()

* getSchemaNames()

* mock(BackendConnection.class)

* new ShowDatabasesBackendHandler(backendConnection)

* modify setUp()

* modify setUp()

* !authorizedSchemas.isEmpty()

* trimResults()

* isAuthorizedSchema()

* modify isAuthorizedSchema()

* isAuthorizedSchema(final String schema)

* rename to ProxyUser

* rename to ProxyUserYamlSwapperTest

* modify examples

* use ProxyUserYamlSwapperTest

* use ProxyUser

* use ProxyUser

* Proxy user YAML swapper

* rename to ProxyUserYamlSwapper

* use ProxyUserYamlSwapper

* ProxyUserYamlSwapperTest

* USE YamlProxyUser

* rename to YamlProxyUser

* use YamlProxyUser

* use YamlProxyUser

* rename to  YamlAuthenticationConfiguration

* rename to YamlAuthenticationConfiguration

* use YamlAuthenticationConfiguration

* use YamlAuthenticationConfiguration

* rename to YamlProxyUserConfiguration

* use YamlProxyUserConfiguration

* use YamlProxyUserConfiguration

for #1941, merge MySQLConnectionIdGenerator & PostgreSQLConnectionIdGenerator to ConnectionIdGenerator