Adding the YouTrackIssueTracker class and the necessary settings.

references #17
Merge branch 'master' of https://github.com/JakeGinnivan/GitReleaseNotes into issue/youtrack
Updating the YouTrack default filter
Implemented (but not tested) the YouTrackApi.
Adding the YouTrack issue tracker instantiation

references #17
Fixing the REST API calls to be the correct ones.

references #17
Adding last date/time that an issue was updated. We assume that this is the closing time (but that may not be accurate if issues get changed after closing them).

references #17
Updated to use the last resolved time for the issues.

references #17
Merge pull request #29 from pvandervelde/issue/youtrack

Add YouTrack support
Removed .received.txt file
Fixed some tests