hookup_manager stage one:  New tables for pending and active hookups (pair programming events)

relates to pivotal stories "display list of pending events in a table", 75025008, and "display list of active/live hookups (i.e. hookups with live hangouts) in a separate table",75025492. 
@yaro: This will be a significant change.  Given the size of this PR already, the new event_instance class addition should go in a new feature/PR, right?