Created CRUD for entity ServiceProvider
requested to merge helmholtz-cloud-portal/franzstephan/helmholtz-cerebrum:crud-serviceProvider into master
Motivation: The API should provide a functionality to create and modify ServiceProvider.
Modifications: Created the ServiceProvider model. Added the controller class and the repository interface.
Result: Now it's possible to create, read (single or multiple (+PagingAndSorting)), update and delete ServiceProviders via REST API calls.