M101: exclusive access for mission execution

As suggested, the exclusive access request is based on the ORG.acquire_resource call (and not via the negotiate call). However, there's some ad hoc mechanism to get a negotiation_id that is required by the acquire_resource call. More details in the code comments included in this PR.

@mmeisinger / @edwardhunter please review.

(this PR replaces #2138, which was taking me much time trying to update)