New: Enable/Disable RSS Sync/Searching on a per indexer basis

@Taloth a few things to note:

- Renamed SupportsFeed to SupportsRss (felt it fit better with what we call it elsewhere)
- Renamed SupportsSearching to SupportsSearch (I assume this will affect torrents) - Fits better with RSS instead of RssSyncing
- The migration explicitly sets searching on Womble's to disabled, we may want to add to this for torrent users, if there are non-search enabled trackers so its not enabled for them and doing nothing

I've been running this for a few days with no issues.