[UPSTREAM] Make the forum subscribe to userjoinsgroup events to automatically subscribe users to forums.

Triggered, guess when - when a use joins a group!

[UPSTREAM] Add a hidden value to the interaction edit form to signal when the interaction has just been created.

If the option is set to yes and the forum has just been created, we subscribe all users in the group immediately.

An event handler (for new event type 'userjoinsgroup') will handle this options.

[UPSTREAM] Add plugintype/pluginname values to the interaction config form, so that plugins can use help for their configuration forms.

A previous commit added the low level stuff for this.

Moved group type help files to the correct location and updated their text to match how groups work in 1.1.

The UI for this still needs to be implemented.

Focus the correct tab even when the group is being viewed by a non member. Also don't show the forum tab when the forums are not viewable.