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
The update script should automatically adjust the log level when updating. Can you take care of this?

0 => 100
1 => 200
3 => 400