Change mentions of 'supporter' to 'benefactor'

One-sentence description

Change mentions of 'supporter' to 'benefactor' for begunstigers

Why?

It is the translation we use in all official documents that was decided upon by the Translacie.

Current implementation

We use several different names for the 'begunstiger' membership type.

Desired implementation

Always use 'benefactor' as translation.