[PVR] added a unique id for each recording, valid as long as xbmc isn't reset
[PVR] added a unique id for each timer, valid as long as xbmc isn't reset
[PVR] let CPVRRecording implement ISerializable
[PVR] let CPVRTimerInfoTag implement ISerializable
json-rpc: add PVR.GetTimers, PVR.GetTimerDetails, PVR.GetRecordings and PVR.GetRecordingDetails
Merge pull request #4246 from Montellese/jsonrpctimers

JSON-RPC: support for fetching PVR timers and recordings