hookup_manager stage one:  New tables for pending and active hookups (pair programming events).  Pivotal #75025008, 75025492

** Please accept the "Event-datetime-migration" first **
New tables for pending and active hookups (pair programming events).
Pivotal stories:
 "display list of pending events in a table", https://www.pivotaltracker.com/s/projects/982890/stories/75025008, and 
"display list of active/live hookups (i.e. hookups with live hangouts) in a separate table",https://www.pivotaltracker.com/s/projects/982890/stories/75025492. 
Added a hookups view, a hookups controller with an index service, and several methods to the events model to distinguish pending, active, and expired events.
does it make sense that something can be `started` and `expired` at the same time?