qualities: rank aac lower than ac3

When the audio track is encoded with AAC, it is not uncommon for it to
be stereo only. On the other hand, the DD5.1 tag usually translates to
an AC3 audio track.

Therefore, rank an AAC encoded audio track below a DD5.1 audio track.
Add support for 720p50
Prepare v1.2.229.dev
Merge pull request #391 from vbabiy/720p50

Add support for 720p50
Merge pull request #390 from vincentbernat/fix/qualities-aac-priority

qualities: rank aac lower than ac3
v1.2.229