BigBlueButton integration API

Following the integration of the mod_bigbluebuttonbn into core, there is a recurring question about possible other usage outside of the context of the activity (maybe as a filter or as a calendar user event..) and ways to extend its current implementation.

The aim of this ticket is to regroup improvements that would make the implementation more generic and ready to use by other plugins or extension:

• Have a well defined API to :
  • Create meeting
  • Join meetings
  • Retrieve meetings recordings
• Add "hooks" and rework on events to allow for more flexible extension points

One of the question here is about location: ultimately this would need to be taken out of the plugin (and used by the plugin as a API "client").