Refactor backend structure

by storing route logic into controller
Fix registration

before this commit, it was not possible to register without a gravatar mail address.
Implement GET /user route

as session getter.
Merge pull request #5 from tobiasmuecksch/master

Fix registration
Refactor user controller

to remove debug output
Refactor user controller

to use Flight::json() instead of echo json_encode().
Merge pull request #6 from tobiasmuecksch/master

Implement GET /user route
Merge branch 'upstream/master'
Use the new functionality splitting conventions