Add hooks into the controllers

[stof]

The controllers should dispatch events in several places of their workflow to provide useful hooks. This would allow people to customize things without copy-pasting the whole controller action for a little change.
the handling of the confirmation email when registering should then be moved to a listener instead of doing a if in the controller to handle both cases (enabling the confirmation would simply mean registering the listener in this case).
These events should also make #552 possible.

I will work on it soon. If you have an idea about a place where a hook could be useful, please leave a comment.

[stof]

#387 may also be simplified using an event. This should be investigated.

[stof]

Done in #867