Comp join

https://www.pivotaltracker.com/story/show/57277068
https://www.pivotaltracker.com/story/show/64099684

Review at http://workoutwars-review.herokuapp.com

There is one issue where the competition creator joins after leaving and the button flashes. I spent over 2 hours trying to figure it out with no success. I created a bug for it here (https://www.pivotaltracker.com/story/show/64538940). But I think competition creators will leave their own competition so infrequently that this can be thrown into the ice box for later. Also it makes no functional difference.