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
A few nitpicks:

1. It is not really clear who "ownCloud" is. Is the company meant, the project, etc?
2. In most jurisdictions the developer still has the copyright on the file. Not sure how it is in the US but you might change this either to your name or "ownCloud Inc."
(see https://github.com/owncloud/core/blob/6d94fc846d1a0ec2d4515f2715317778a5269223/lib/public/backgroundjob/ijob.php#L3 for an example)