Connector Groups duplicating membership

Group ID's are being duplicated on connectors when modifying group membership, and not being removed on deletion.

Reproduction steps:

1. Create multiple connectors
2. Create connector group
3. Add a few connectors to group. Save group
   1. At this point, note the configuration file adds the group ID to the connector configs
4. Modify group again, adding another connector
   
   1. At this point, note that the original connectors added to the group now have two entries for group ID in the connector config. The new connector has one entry for group ID.
5. Modify group again, removing one of the original connectors
   1. At this point, note that only one of the ID's is removed from the configuration
6. Modify group again
   1. At this point, note that the connector removed in the previous step is still marked as being a member of the group
7. Delete group
   1. At this point, note that group ID's do not get removed from the connector configuration.