BIG update to Antenna

I've spent most of today completely refactoring Antenna. While the biggest change is mostly noticeable for me (improved maintainability), I also added one feature by popular demand:

When entries are added the database now keeps track of which feed they're added from, and if an entry is removed from a feed and the feed is re-submitted that entry will also be removed from Antenna.

I've tested the code as best I could, but please let me know if you find any bugs.

-- CC0 Björn Wärmedal