rebase of the code in pull-request #253 (flattr queue and autoflattr support)

I ginally found the time at 30c3 to rebase the flattrqueue and autoflattr code (see prior pull-request #253 and feature request #87) onto the current Antennapod develop branch, in order to keep up with the changing database layout and code, would be great if you got around to merging this eventually, though...

Happy new year...