Minor code cleanup.
Add ability to updatePassword to angular.js.

* Add updatePassword to userService.js
* Add updatePassword function to userSettingsPanel.js
* Update userSettingsPanel.
Add UserMailer class.

I'm also adding an email for password_changed method.
Add PATCH action to update password on users_controller.
Display errorMessages in the template, if any.
Code cleanup.
Do custom checks for password and password_confirmation in users controller.

TODO: this needs to be moved to model layer.
Remove unecessary params from user_params.
Change devise password length validation to minimum of 6.
Fix how we display errors in the view.
Fix bug where function def was incorrect.
Add newlines to password_changed email.
Add more newlines to email!
Bundle install active_admin.
Run rails g active_admin:install (excluding CSS assets).
Add active_admin assets (CSS, JS), and commenting out CSS.
Scope the authentication keys to User model.
Scope authentication failure class for Devise.
Remove require_tree . from application.css

This allows us to add in active_admin css.
Run rails generate active_admin:resource User