get unittests to compile with new FlattrStatus()
Re-enable support for the "Flattr this app" item in Settings
* directly update Feed/FeedItem FlattrStatus instead of writing back entire Feed/FeedItem to database
* fix race condition when fetching FlattrStatus
* fix missing copy of Flattr status in Feed.updateFromOther()
* fix feed reading from db, was missing FlattrStatus

followup on #331
Load only Flattrables in flattr queue from the database.