Removed the dummy monitoring page.
Improved the behaviour of scheduled lessons.
* If a lesson is already scheduled and we get another request to schedule it, the second request is ignored. This stops a double submission throwing an exception (quartz would end up with non-unique job names).
* If a lesson is already started and schedule is called on the lesson, an exception is thrown.
* If a lesson is already started as start is called again, then the second start is ignored. This will occur if a lesson is scheduled, then a user goes into monitoring and starts the lesson straight away. The quartz job isn't remove so some time later start will be called again.
