Implemented model for Event

I added an implementation of the event model, which would resolve issue #31. An event has a date and is currently only available to be updated using the admin panel. The box on the front page (and join_us page) selects the next event or automatically generates an event based on the first tuesday of the next month. Also, the code for that box was moved to a partial called event. There's a starting point for an event controller, but I haven't done anything with that yet. I want to get an ok for this before proceeding... and feel free to comment and make me change anything that looks ugly or messy.