Create reminders

* Move back end url to config to facilitate changing environments.
* Create reminders

@codeforamerica/denver this is the first hack at this. It needs some iteration. Start thinking about:
* The email/sms wording.
* The location and styling of error message.
* The feedback to the user when reminders are created.
^ These are just a few examples of where I through in a first effort for us to think through later.