Starting rewrite of how the RSS works

This hasn't been tested at all and there's a lot of things that need to be rewritten.
I've just made some dirty hacks to get it to build.
This introduce feed groups into core, and start working on deserialization.
Fix build
Better deserialization of Feed groups
Changed the parsing for feed groups
Fix various crashes
Fix duplicated separator on saving filters
Merge remote-tracking branch 'origin/wip/rss' into wip/indev