Random Event Overhaul

Alters the event controller based on http://baystation12.net/forums/viewtopic.php?f=5&t=10706.
Exception is that there is always some start time variance to prevent metagaming (unless configured otherwise).

Mundane, moderate, and major events run on their own timers and start and run independently of each other.
Multiple events of the same severity degree can run at the same time. 
Currently only one instance of the same event can be active at a time.

The carp migration event has been slightly modified to show how the same event type can be used for multiple severity levels.

**Remaining**
- [x] Add existing events to appropriate event categories.
- [x] Complete the implementation of making configurable event delays.
- [x] Admin tools for working with the event manager.

**Optional for this particular PR**
- Implement some or all of the new suggested events.