Enforce data types attached to sponsor benefits

Fixes #165.
Feedback on financial aid applications

* The PyLadies grant is only applicable to women. When applicants select that grant and sign up for a hotel the "sex" defaults to women.
* Add some default text to the effect that the PyLadies grant is only available for women.
* When someone submits an application the PyCon list should receive a notification. NOTE: it is already the case that the applicant receives a notification that their form has been submitted.
Don't redirect forever if the registration URL has not been configured
Merge pull request #165 from caktus/feature/165-sponsor-benefit-validation

Enforce data types attached to sponsor benefits
Merge branch 'develop' into staging
Merge branch 'feature/166-feedback' into develop
Merge branch 'develop' into staging