JSON-RPC: Basic EPG support

These commits add basic EPG support to JSON-RPC.

Since this is a feature I'm really missing, I decided to add support for two basic EPG methods to the JSON-RPC interface: I've added the methods PVR.GetChannelProgram and PVR.GetBroadcastDetails to the PVR namespace.

- PVR.GetChannelProgram: Returns the program listing for a given channel denoted by the channelid. Properties can be selected, so that it is possible to have e.g. the "starttime" in the full listing.

- PVR.GetBroadcastDetails: Returns the details for a single broadcast denoted by the uniqueBroadcastId, which can be retrieved from the PVR.GetChannelProgram listing.

I had to extend the FileItem for EpgInfoTags and decided to add the EPGSearchFilter option for searching by uniqueBroadcastId.

This has been my first time after a long break working with C++ and my first time ever coding for XBMC, so please be lenient. I tried my best to give it a good shape and am willing to work on it until it's worth to be a part of XBMC. Changes and additions on request. I'm looking forward to this being an addition to the JSON-RPC based remotes like "Yatse"...