Added login and logout features. More styles too.

- Login and logout requests are not implemented.
- Logout is a GET request. I've never noticed how weird that is before.
- Styles for simple forms, like login forms, are in place.
- A permissionTo global function was defined in app/start/global.php, which
takes a User model method name (supposed to be one of the can* methods) and
check for (1) if there is a logged in user and (2) if a call to that method
name returns true on that user. The function returns (1) && (2).
- Some more pages templates were added and/or adjusted.