Remove unused toolbar group name.

Can't see why we'd need to style toolbar groups differently.

Change-Id: I0646b8cf37ab19e34a8ed2eb8558773365403610
Make MW meta dialog experimental

Also remove the exception thrown when we try to add an non-existent
toolbar button, as it may just be experimental and not loaded.

Change-Id: I0a60421f45d7a3941c510defc60d1fbf9469e784
Merge changes I0a60421f,I0646b8cf

* changes:
  Make MW meta dialog experimental
  Remove unused toolbar group name.