"finalizing" the OpenMeta plug-in

Thought this would be quick and easy. It never is. :-) Anyway, this should be all the stuff discussed in #1 and more.

  * name and icon improvements
  * plug-in metadata improvements (related bundles and paths, requirements, bundle ID)
  * tags in the third pane are pulled from the catalog
  * when tags are set/added/removed, the catalog is updated immediately (no need to wait for the next rescan)
  * regular tags aren't overwritten by "transient" tags when right-arrowing into a tag
  * added to the documentation

And I'm probably leaving some stuff out. Look it over. If you're OK with it, I'll get this thing released (finally)!