Common contact role form & page permission fixes

As I accidently merged !257 (merged) too early, I opened this MR to create a shared component for contact role assignment.

Goal of this MR:

• add a form component for the assignment of contacts and roles to devices / platforms / configurations
• fix issue with error messages "you're not allowed to edit xyz" when reloading a page #279 (closed)

Fixes also #279 (closed)