Add option to invert role selection for trigger.

[krostas1983]

As lifecycletrigger_byrole has a handy delay function to delay setting the trigger off, we wanted to use it with a "watchdog" role like "Authenticated User" which is not present in any course ever. Unfortunately, this would not be limited to any courses outside our desired category (set up in a parallel trigger), as each trigger works independently of others. The delay would then begin upon activation of the workflow...

We liked the idea of a watchdog role, however. We created a category enrolment for that role within our "trash" category and added the option to invert the role selection for this trigger. In this way this trigger can be used as:

• a simple delay trigger
• a category trigger
• a manual trigger (if teachers are allowed to assign this role, possibly to themselves)

[NinaHerrmann]

Looks reasonable to me - could you add a PHPUnit test for maintenance? 🙂