MTVIE: fix xml tags in the media namespace (python2.6)
GametrailersIE: make it a subclass of MTVIE to reuse most of the extraction process
Implement format selection in YoutubeDL

Now the IEs can set a formats field in the info_dict, with the formats ordered from worst to best quality. It's a list of dicts with the following fields:
* Mandatory: url and ext
* Optional: format and format_id

The format_id is used for choosing which formats have to be downloaded.

Now a video result is processed by the method process_video_result.

Implemented in TEDIE.
ArteTV: implement multiple formats
Implement the max quality option in YoutubeDL
Do not handle format selection for IEs that already handle it
Default 'format' field to {width}x{height}

If width is None, use {height}p and if height is None, '???'
ComedyCentralIE: use the new format selection system.