Editor: Set a filter (like project::added) to each table.

This would make things easier, many mods do add new content and change little existing content. It would be nice if I could say: only display stuff that is handled by this mod. E.g. MWEdit (only) supports this behaviour.

(RM-2532 from redmine: created on 2015-05-10 by Who Knows, )

Edited by redmine