Presentation and session management

This adds

* Session management (login/logout)
* Password resets (which everyone will need to do in order to setup their password in the first place)
* Presentations

## What's Left

**This is not ready to be merged!** We still need to:

- [ ] Style the new views
- [ ] Update the password reset email
- [ ] Style the flash messages
- [ ] Add button a way to say that you are attending a presentation (I'm not 100% sure how this should work)