Midgetspy backports

Various backports from midgetspy:

* Attempt to get quality from snatched episode status
* tvdb_api update
    * Skip episodes which are missing SeasonNumber or Episode Number (or DVD_season or DVD_episodenumber)
    * Avoid excessive calls to the ShowContainer garbage collection
    * fix ShowContainer cache resizing
* Adding webm as a supported extension
* Only log deletion when we're really deleting