Adds admin to User; adds admin bar

* Changes ```current_user``` to user object not just user id
* Changes ```current_project``` to project object not just project id
* Eliminates redundant password attribute in User class
* Adds profile link to nav bar
* Adds admin boolean to users table
* Adds ```admin?``` helper method
* Adds admin_bar for signed-in admins
* Changes unordered list of user stories to multicolumn div with child divs
* Modifies stories CSS