Documentation update
Add 32/64-bit JVM check to Windows batch file
Add MPV check and bump version number
Remove playback option incompatible with some versions of mpv
Mac GUI fixes

Fix radio button widths in PreviewPanel
Fix position of mpv window
Work around Mac OS X loss-of-focus problem for slice preview

Make slice-previews audio-only on OSX to avoid the X11 window stealing the focus from Postslate.