ActivityIntermediator.TYPES doesn't allow plugins to use activities
|federation, activities, plugins
With #905 we now have the activities that can be created when the user does something on GMG. However there is a fixed TYPES dictionary which doesn't allow plugins to add their models as objects which take part in activites.
The way this could be changed is to have a ActivityTypes table which is this map. The current TYPES can be populated by the FOUNDATIONS system and plugins can add themsleves to this table.