Twilio integration

Commit 2f21a6a is valuable and should be read here!

Twilio is up and running.  It just needs to be thrown into Heroku.  It can be tested by running `rake text_users` (one can run `rake text_users --trace` to see detailed running information) and by ensuring that the users associated to the reservations that currently exist have phone numbers.
>I'm implementing the logic to skip non-phone-number-having users.  This way it can be optional.
>>We should look up implementing a security feature that securely stores cell phone numbers and email address...I don't know if devise does this.

I have Heroku set up and ready to receive our custom rake.  I just don't want to set it up because the rake does not exist on Heroku and that's just an infinite loop waiting to catch us.  We can wait until later for that.