Use episode thumbnail on springboard when launched from On Deck, fixes #240.

Slightly annoying, but we basically keep track of both sets of URLs and then
have the springboard screen change the master URL when it loads and when it
closes.
Add preferences for looping audio playback.
Tweak buffering->playing timeline transition.

For HLS, the Roku reports isStreamStarted when it downloads the M3U8, not when
it has started actually playing the video. So we now leave that in the
buffering state and only transition to playing when we get a playback event.
Try to differentiate between channel search and text input.

The Framework doesn't do us any favors here. Channel developers say they want
some text input and the XML says it's a search item. If they say they want a
search, that's also a search item in the XML. On the Roku, we now clumsily
try to differentiate based on the key (is it a search service?) and the
prompt. If it looks like a text input, then we use a keyboard screen instead
of the search screen. The keyboard allows for more characters and has no notion
of progressive search, so incomplete text won't be sent to the channel.

In order to pull it off it was also necessary to tweak how posters decide if
they should show a message about empty containers.

And in other news, we're down to one available function again. :[
Bump version to 2.6.5 and add release notes.