Provide the codebase of plugin tests. Make the plugin test in the CI loop.

* Support Gateway without agent

* Remove the meta file

* Change OAL generator tool to runtime.

Step 1. change project structure. API links and maven pom.

* Part of metrics class generation

* Metrcis class generated.

* Set up the basic structure of new OAL engine.

* Finish metrics generation.

* Support dispatcher generation.

* Format codes.

* Generate dispatcher all methods.

* Implement disable in hardcode.

* Clear up

* Fix compile startup.

* Update license and document of new OAL engine.

* Fix rat.

* Disable class output in default

* Copy from @kezhenxu94 's test PR, https://github.com/apache/skywalking/pull/3110

* Wait for the mount command to finish

* Support sampling trace at server side and keep metric right.

* Add a trace sampling document

* Fix wrong default value.

* Fix document issue.

* Fix assemble issue.

* Fix wrong settings and doc.

Add a new assembly xml file to oap-starter project, and add `oapService.sh/bat`
files to apm-dist project.

Remove `collectorService.sh/bat` scripts from apm-dist project.

* Refactor the old ComponentDefine and ComponentsDefine to be based on file for better extenable.

* Support don't uplink componentId, but componentName in segment.

* Fix CI.

* Move component id exchange logic from SpanDecorator to SpanIdExchanger.

* Fixed the compile error cause of class construct changes.

* Collector instrument agent.

* Make the agent.jar output to the /agent folder in collector package.

* Try to add metric annotation.

* Change the instrument ways.

* Reformat.

* Finish the agent codes. Wait for @peng-yongsheng 's metric requirements.

* Debug new instrument.

* Fix a detect bug.

* Finish the instrument

* Fix compile issue.

fixed maven 3.3.9 build issue caused by empty assembly ID on Ubuntu 16.04.2 using OpenJDK 1.8.0_151.

[INFO] Building apm-collector-boot 5.0.0-alpha
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ apm-collector-boot ---
[INFO] Deleting /home/steve/skywalking/incubator-skywalking/apm-collector/apm-collector-boot/target
[INFO] 
[INFO] --- maven-checkstyle-plugin:2.17:check (validate) @ apm-collector-boot ---
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.492 s
[INFO] Finished at: 2018-02-18T12:05:49-06:00
[INFO] Final Memory: 19M/235M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-checkstyle-plugin:2.17:check (validate) on project apm-collector-boot: Failed during checkstyle configuration: cannot initialize module Header - Unable to find: CHECKSTYLE_HEAD -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException