Support for special days

[funkenstrahlen]

Special Days are days on which only a special selection of episode are played on a channel. Example: Movie day. On this day only movie related podcast are played.

Add new special days: channel, date, title, subtile, image

This should include:

• scheduling special days => date, title, describtion, banner image
• show banner message on index page and on the channel page that features the special day