Merge remote-tracking branch 'upstream/master' into system-log-prepare-table-on-each-flush

#2131 deleted excessive logging

Revert "#2131 deleted excessive logging"

This reverts commit d78a46d9.

Revert "SystemLog: execute prepareTable()  on each flush"

This reverts commit 7f60bb0a.

SystemLog: execute prepareTable() on each flush

* Macos test fix

* Fix freebsd build

* CLICKHOUSE-3553 Rebuild loggers on every config change

* rename clickhouse_common_configprocessor -> clickhouse_common_config; move Server/ConfigReloader.cpp -> Common/Config/

* CLICKHOUSE-3553 Set new level to all loggers on reload

* Dont use hash

* Update BaseDaemon.h

* Make separate libs Common/ZooKeeper and Common/ConfigProcessor
renamed:    dbms/src/Common/StringUtils.h -> dbms/src/Common/StringUtils/StringUtils.h

* Fix space

* Fix data in system.build_options

* merge

* merge

more consistent ISecurityManager interface: return shared pointer to User to prevent race conditions with loadFromConfig

- We add BackgroundSchedulePool which can execute a function at a specific point in time. Basically all tasks are added in a queue and precessed by worker threads.
- The most important difference between this and BackgroundProcessingPool is that we have the guarantee that the same function is not executed from many workers in the same time
- Each of the following classes instead starting a thread will register a task in BackgroundSchedulePool and when they need to run will call schedule or scheduleAfter(duration) functions

This commit is moving all threads created by ReplicatedMergeTree to BackgroundSchedulePool tasks

NOTE: I did a minimum number of changes to be much simple to review the code

This addresses one of the remarks in the PR.

All format schemas are required to be in the <format_schema_path> directory.
This makes loading schema files less tedious, as the path can be omitted.