New: Public display of EMPTY future playlists

Empty future playlists are now displayed in Spinitron public pages including in the calendar, in lists of playlists and as a playlist page, so long as the Display as a future public playlist checkbox is checked.

Until now this checkbox worked to display future playlists only if they had some content, an episode title, episode description, or at least one spin.

Note: a future public playlist preempts scheduled shows in the public calendar display.