bz19835: increased min-width or some list-view columns.
bz19835: increased min-width for the date column
bz19828:  Don't let PlaybackManager.get_playing_item() return None

It seems that many pieces of code rely on this and some of the newer
playback changes have removed that guarentee.  Fixed it so that if we
filter out the currently playing item, get_playing_item() still
returns the ItemInfo object.