Add filters

[janboddez]

I sometimes prefer to have an item's author name replaced with the name I gave the feed, for instance, although the icons help a lot recognizing the individual feed.

But I still might wanna "correct" longer or faulty names/feeds, etc.

So, make item name and author filterable, and then we'll see about everything else.

[janboddez]

Name and author are filterable (upon set rather than get, because speed, etc.) as of 19e15c7.

[janboddez]

This doesn't seep through to the mf2 JSON we store, however. (But we don't yet offer Microsub, anyway.)