Optimize the activemembers admin

Ghost Userrequested to merge
fix/faster-activemembers-admin into master

Closes no issue.

Short description

This MR makes the activemembers admin a lot faster by doing the following two things:

  1. Add member to raw_id_fields in the inline for committee memberships. Before the entire list of members was copied for every committee membership. This resulted in html pages of several megabytes.
  2. Remove duplicate queries (for different ids) by adding select_related calls in the right places.

Merge request reports