Show selected tags correctlly.

When a new tag is created, the notification for the created tag, could
take some time till it is populated within the TagModel. That's why we
need to update the view if a tag is added. But also if a tag changes his
name f.ex. or that we delete a tag we should update the view.

Maniphest Tasks: T1276
Differential Revision: https://git.kolab.org/D174