Mailing list for societies contact persons

Create an automatic mailinglist for all contactpersons of the societies.

When the contact person of a society changes it is a lot of double work for the new intern to also update the mailing list. (Request from @tvalten)

Create a new automatic mailinglist for all heads of the societies. These people are the contact persons.

Look at how the commitee chair mailinglist is done.

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