Added a .css.less file to override default bootstrap styles. Included padding to accomodate nav bar
added admin namespace including home controller and view for future admin control panel
generated roles model for cancan authorisation, including specs
added index to roles and created RolesUsersJoinTable for HABTM relationship
added HABTM relationships to user and role model
renamed column roles to name in roles table to avoid confusion
changed role model to adopt change to the migration
added default admin role to the seed file, made default user admin in seed
added admin ability to cancan ability.rb model
Error handling for cancan 'access denied' error
cleanup routes.rb
Made the admin home controller only accessible by admin users

Basic authorisation in place.
- added a method to the user model to check for role names
- changed the ability class to prevent non-admin users to read the index page
  - TODO: make cancan recognize namespaces as described on the cancan wiki
- made admin index page state so
added link to admin control panel to the navbar, only visible for admin users
Simplified things in the admin interface

CanCan abilities are not needed for current (non)functionality.
Therefore, a base controller for the admin namespace is created,
just verifying that the current user is in admin role.
If not, user is redirected to home page with error message.
admin/home_controller is subclass of this base controller.

once cancan abilities will be needed, it is simple now to add
separate abilities per namespace.
see https://github.com/ryanb/cancan/wiki/Admin-Namespace for details.
Merge branch 'feature/admin-panel' into feature/user-management

Admin Panel basics are in place!