Add Controller and view for login
Add library Shibboleth_authentication_service

Shibboleth_authentication_service provides functions to
check if a shibboleth session exists and if a user is
in the db table for users
Update controllers to implement authentication

Update controllers Admin, Login, and Manager to use
Shibboleth_authentication_service and redirect accordingly
Rename file User_model according to CI standards
Add class User_mapper
Rename controller Login to Auth
Minor changes to User_mapper and User_model
Update authentication via shibboleth
Add custom loader class ELK_Loader
Adjust columnnames in Crud_service, add function getUsersCrud()
Add views for access request
Merge branch 'master' of https://github.com/ELK-Phil-UZH/roselit

Pulling in changes from master