pvr: Added API function GetRecordingEdl

@dteirney: This will be probably of interest to you

This PR extends the PVR API with the function GetRecordingEdl to retreive edit decision lists from the backend.

In addition DVDPlayer's EDL class has been adapted to read the EDL from the backend for recordings.

A sample implementation for the MythTV PVR addon can be found here:
https://github.com/fetzerch/xbmc-pvr-addons/commit/3c6738a9837636b1b649fee7a87778a9f576c250