Move some prefs under the new-ish Audio Prefs screen. h/t @ljunkie

It's kind of a tossup, since the prefs *are* advanced. But now that we
have an audio prefs screen anyway, it makes sense for these to live
there.
Add a toggle for DTS support, fixes #267.
Only use the universal transcoder with items that have streams.
Make sure we have video details before trying to play, fixes #265.
Don't Direct Play when first stream is unsupported surround sound.

It's too likely that the stereo stream coming after the surround sound
stream is commentary. And we can't always trust the Roku to choose the
right stream anyway.
Update Makefile and README for recent changes.

My Roku is now requiring authentication on installer requests.
Bump version to 2.6.8 and add release notes.
Fix crash in adding server manually.
Merge remote-tracking branch 'upstream/master'