Updated logging system.
Improved logic for discovery of current Git ref.
Updated plugin definition macro.
Changed information for VCS loading.
Added a CMake module for Git.

  * Defined method 'git_invoke'.
  * Defined method 'git_grab_ref'
  * Defined method 'git_current_branch'
  * Defined method 'git_current_ref'
Removed Git polling from WintermuteVersioning
Merge branch 'feature/extensibility' into develop

* feature/extensibility:
  Removed Git polling from WintermuteVersioning
  Added a CMake module for Git.
  Changed information for VCS loading.
  Updated plugin definition macro.
  Improved logic for discovery of current Git ref.
  Updated logging system.
Dropped unnecessary private header for logging.

  * Removed includes to private header.
  * Moved definition of LoggingPrivate into source.
Corrected definitions in Wintermute::Application.