Revert "Stop listening to kernel.exception."

This reverts commit 4a3fc0f5db46cf24316c2d849e85cab23a5f0b77.
Revert "Convert HTTP errors to JSON responses if necessary."

This reverts commit 15983a5f1ea638a1b87ffb63bcf077152756bfcc.

Conflicts:
	src/Surfnet/StepupGateway/ApiBundle/Resources/config/services.yml
Respond with 401 w/ JSON when authentication fails.
Switch to entry point bugfix branch.