User registration

- [x] Implemented RegistrationController
- [x] Created registration template 
- [x] Implemented input data validation on front-end
- [x] Created Sinatra routing required for registration
- [x] Added OPTIONS method for Sinatra required for CORS POST requests
put to controller or (better) to service:
``` javascript
$scope.doesPasswordMatch = function() {
    return regform.password_confirmation.$dirty && regform.password_confirmation.$error.dontMatch
}
```