Added is_active_tac service

Added is_active_tac service, tests, and secondary tests on list_proposals that trigger the use of is_active_tac from within get_visible_proposals. Also, I changed permissions on the list TAC members endpoint to all roles.

When reviewing, please give some thought to mixing in an application layer service (is_active_tac) from common into the domain layer service (get_visible_proposals). I know we try not to do this when possible, so let me know your thoughts on if I should, at least, move is_active_tac to a common domain layer service.