Add action to update metadata group after its creation.

Metadata groupowner is defined when user create a new record. There was no option for the metadata author to easily update the groupowner. This action is added to the editor toolbar to choose the group to put this metadata in using a dropbown button containing the list of groups.
Merge pull request #450 from fxprunayre/feature/metadata-group-update

Add action to update metadata group after its creation.