[WIP] Login System

### Scenarios:
- [x] User logs in with nothing -> "Please enter your username and password."
- [x] User logs in with either username or password missing -> "Please enter your username and password."
- [x] User logs in with wrong user/password -> "Wrong username and/or password"
- [x] User logs in with a non-existant user -> "Wrong username and/or password"
- [x] User navigates to /mycell when they are not logged in -> redirect to /login & "You must be logged in to view this page."
- [x] User navigates to /login when they are logged in -> redirect to /mycell
- [x] Logout button only appears when logged in
- [ ] User clicks logout on any page -> redirect back to that page

![Optimal cereal eating](http://31.media.tumblr.com/581a4d2868b42e905452b7dc9cbbd4a4/tumblr_mqquqzz2N91qznvrxo1_400.gif)