model: release_seq synchronization generates mo_graph edge "work entries"

model: release_seq synchronization generates mo_graph edge "work entries"

Now, when the synchronization for a ModelAction is updated while resolving
release sequences, the affected ModelAction(s) can be queued to the work_queue
for later processing (i.e., checking for mo_graph edge additions).

Note that the MOEdgeWorkEntry is not yet handled in the work_queue loop.