Related names
Offloaded creation of slug to mixin

This mixin is used by both, the Session and Camp classes, and can be
used by any other classes that require slugs
URL scheme amended so it works with the login_required decorator
Use only 1 query for retrieving session with differentiated 404 messages
More info in admin
Require login for dashboard view
More optimizations
Camp template: link to create session and list of sessions
Dashboard template: list of own sessions
Session view template: Link to camp
Implemented post-login/register redirect