Vote Delegation: new setting to prevent principal from voting

[MSoeb]

Description: Currently, principals can vote even though a vote delegation is active. This should be improved and prevented by a new function.

What should happen:
If a vote delegation is active, principals should not be able to vote. Only the proxy holder should be able to vote for themselves and the delegated vote. A new setting should be integrated to enable this.

[Elblinator]

waiting for OpenSlides/openslides-backend#2370

[jsangmeister]

waiting for OpenSlides/openslides-backend#2370

done