Add Ability for Users to Reset Their Own Passwords

[danloveg]

It is currently impossible for a logged-in user to reset their own password. This functionality should be added so that it's accessible from the Profile page.

[danloveg]

Adding some more detail:

• The UserProfileForm should get three new fields:
  • current_password
  • new_password_1
  • new_password_2 (Re-enter the password to confirm)
• UserProfileForm should be moved out of admin_forms.py, it doesn't make sense for it to be there
• The form should pass validation if none of those fields are filled out. Only if any of them have content should validation run against the fields.
• The form fields should be rendered in a new "password reset" section in the <form> in profile.html.
• After submit + validation, the user's password should be changed (see: Changing passwords)