Users can now mark individual cards with one of four different coloured
flags, instead of relying on a tag that applied to the whole note.
- replaced marking functionality in reviewer and browser with new
flag options
- added flag:x search
- marked and leech tags now show in normal tag list in filter screen,
instead of being treated specially
- the other clients will need updating to set and shown the flags, but
flags set in the beta should be preserved by the other clients
