Add a str function to Grid.

Debug messages are so much more informative now.
Fix overlapping events issue.

Fixed an issue where an event would register more events to a list that
was currently being iterated through. Now uses a temporary list so that
iterators are not invalidated.
Add FLOCK_UPDATE event.

Because we need more events. Actually, now flocks can change their
component entities... kinda necessary for recalculation.
Add responder to CREATE_ENTITY events.
Complete the logic of the clustering system.

Use the FLOCK_UPDATE event to actually use the results to create cloud
groups.