Adding monolog

Fixes:
https://github.com/owncloud/core/issues/8956
https://github.com/owncloud/core/issues/9083

Adding Monolog to replace exisiting logging methods which adds much more robust functionality with very little alterations to current work flow

Changes to current workflow:
LogLevels have changed by 100
Format of log has slightly changed.


Also see https://github.com/owncloud/3rdparty/pull/114
Can we please keep the log levels? This will be a nightmare otherwise. In addition I see no real need to have more than these 4 levels.