Move method and its dependants from Controller

[Valefant]

HelpProviderController#acceptEmergency should be moved to EmergencyController.
The same goes for the associated service HelpProviderService#acceptEmergency.

The tests which we have written so far should then be adjusted too.
HelpProviderControllerTest#testAcceptEmergency to EmergencyControllerTest
DefaultHelpProviderServiceTest#testAcceptEmergency to DefaultEmergencyServiceTest

[ameliadiedrich]

I would like to take care of this issue :)