added uid and category field to hangout model

added UUID to Hangout

added uid to Hangout
updated views and specs to use hangout.category

updated specs for hangout model
introduced generate_hangout_id in hangoutsHelper

updated generate_hangout_id
updated events and hangouts show views and specs to use generate_hangout_id

modified hangout partial to set callback url correctly
updated hangout model and controller code and specs to use event_id
changed Even to have many hangouts
updated event controller and specs to use the fetch the lates hangout
refactored hangouts.js and specs

refactored hangouts.js
added default scope to hangout to order by created_at
changed event to has_many hangouts
adjusted specs to use event.last_hangout