Additional user account views and styling

This is a follow-up to my former PR, includes a few more views and templates for user account management (slowly integrating `django-user-accounts`). I tried to use a more uniform DRY approach to styling.

Password reset doesn't work on accounts that have been created manually. I guess one has to go through the app's registration process.

Now that I've started using it I'm of two minds about keeping using this app or going for https://django-registration.readthedocs.org/en/latest/quickstart.html which I had used in the past. I can't see clear advantages to django-user-accounts and the fact that it apparently only fully works for accounts registered via itself is a bit annoying.