[engine] Add cost qualifiers to places where they make sense.
[scheduling] Untested work on updating the flow graph on resource registration.
[scheduling] Fix deadlock. Whoops. (We may need to move to a recursive_mutex here.)
[scheduling] Fix initialization bugs for flow graph update functionality.
[scripts] Fix syntax error in plot script (seems to no longer work with latest versions of graphviz).
Merge branch 'malte' into cost_model