Mediainfo support

Adding MediaInfo for each EpisodeFile.
For a normal download Import the mediaInfo is retrieved during the import. But for existing files it's delayed and handled later on, hopefully async enough.

I rewrote a major part of the FileNameBuilder logic to give the token replacement code a bit more flexibility.
I still don't like how the multi-episode numbering logic is handled, but it will do for now.

Obviously I also added MediaInfo as naming token:
- Series.Title (unchanged)
- Series.CleanTitle (removes : . ( ) from the title)
- MediaInfo.Video (video codec only)
- MediaInfo.Audio (audio codec only)
- MediaInfo.Simple (video+audio codec, a-la scene)
- MediaInfo.Full (my own concoction that includes audio & subtitle languages)

@markus101, I don't think it's finished yet, but I would like your opinion. Please note that hereby migration 56 is reserved :)
We talked on IRC for asec, but need a decision. I'm okay with either, but we need to be consistent. It doesn't have to be fixed everywhere right now, but eventually during some code cleanup we change everything from Filename to FileName, or FileName to Filename.
We still have .net stuff like System.IO.Path.GetFileName, which we cannot change, but at least our own code should be consistent.
Lemme know which you want.