music/playlist: controls tweak - "select" is main

Limited to music section and playlist (audio + video):
- SELECT to start continuous replay
- PLAY to replay just single track/video
For audio this is essentially a button switch, for playlist video the
preplay screen is lost… (shall it be pushed into scribble menu?)
Make 'PIL/Pillow not installed' item unselectable
Fix xml names - Linux filenames are case sensitive
add "now playing". missing JS to hide item. :-(

there are some (more or less) native functions out there, called
atv.nowPlaying.willStartPlaying/willStopPlaying/didStopPlaying/playerSta
teChanged/currentAssetChanged/currentAsset to create a hiding script…
but I have dumped too much time here, without a result so far. :-(
fix spelling (please re-hide shared libraries, if needed/wished)
new POT - did we really change that much?
PILBackgrounds - disable for iOS prior to 6.0
Fix ByFolder post-play navigation

Reference:
https://forums.plex.tv/index.php/topic/129936-menu-navigation-problems/
Do we really need this “volatile=*” everywhere?
Unplayed/partiallyPlayedDot is not shown in Grid view!
tweaks on aTV2 installation instructions
Merge remote-tracking branch 'upstream/master'

Conflicts:
	assets/templates/Settings_TopLevel.xml