Add MediaTimeRangesType for playback skip or other function

[martinoneutrino]

This isn't much to work with, but I'm hoping it will start the ball rolling on getting commercial skip working on MythTV on AppleTV.
The API for commercial breaks is at: /Dvr/GetRecordedCommBreak?RecordedId=00000&OffsetType=Duration (valid for MythTV 0.28+)
The XML format returned is given at https://www.mythtv.org/wiki/DVR_Service#GetRecordedSeek.
The Cutting/Mark values of 4 (Commercial Start) and 5 (Commercial End); as given at https://code.mythtv.org/doxygen/programtypes_8h_source.html#l00061
The Cutting/Offset values are in microseconds, and so translate pretty easily into CMTime and CMTimeRange values.