implement sessions

[trriplejay]

an authenticated group leader can create a 'session' which triggers a workflow that results in selecting a game, and selecting a date/time.

• how to determine the final date/time from doodle?
• users can vote by ranking the games 1-n. they dont have to vote on every game available, perhaps picking the top 3 would be best.
• use logic described here to tally user votes: https://www.youtube.com/watch?v=3Y3jE3B8HsE
• only logged-in users can vote. we need some way to validate they are who they say they are