Fix import21

Closed username-removed-35210 requested to merge abompard/mailman:fix-import21 into master

This branch fixes the import of some configuration values from Mailman 2.1 dealing with members and nonmembers moderation.

  • The member moderation bit was not interpreted and converted properly
  • The *_these_nonmembers parameters were not imported properly and not taken into account by the moderation rule

All tests pass, coverage is good.