Unification of the user profile, the contributions and the permissions

* Reshaped/added permissions following discussion in https://github.com/my-koop/service.website/issues/300 (Part of https://github.com/my-koop/service.website/issues/346)
* Reviewed the way contributions are exposed/collected
* Added tab-level permissions to the user profile (https://github.com/my-koop/service.website/issues/326)
* Now providing developers with context information when a front-end permission check using the mixin does not succeed (https://github.com/my-koop/service.website/issues/343)
* Now handling the error/success cases a little bit differently when updating the permissions (https://github.com/my-koop/service.website/issues/344)

Plus bug fixes and UI/UX-related improvements. (Part of https://github.com/my-koop/service.website/issues/345)