Initial ClusterCoordinator UI

Refactored the acceptance test for assign cluster coordinator with goal of simplicity (so that others can follow the pattern)

Finished test-driving the un-assign code.

Created a basic UI that allows the administrator to view cluster coordinator assignments for a disaster and assign new cluster coordinators from the registered users list.

The next step is to add un-assign to the UI, then change the user drop down into a textbox with ajax-y autocomplete.