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
We might anyways update this to a constant defined in the logging class. Numbers are always so hard to understand ;)