Specify slim version to use via pessimistic version constraint to ~> 2.0
Specify slim version to use via pessimistic version constraint to ~> 2.0
Add omniauth support, currently only for developer method

Todo: Add facebook support

Workflow: If user chooses to authenticate via omni-auth, we will recieve a callback to the identities controller. Here, we try to either authenticate the user, or if identity is unknown create a new and link it to the identity. Then we ask the user to fill in the required fields (such as city) and confirm name and email.