jQuery Django `CRSF` helper should be `CSRF`.

See the [docs](https://docs.djangoproject.com/en/dev/ref/contrib/csrf/).
It stands for Cross-Site Request Forgery.

**Breaks backwards compatibility!**

It's possible to keep both versions and write tests for each, but you were already using `csrf/CSRF` in some places and `crsf/CRSF` in others, so I made it all consistent.