Implement inhibitor arcs for TPN.
Merge branch 'master' into tpn_inhibitor_arcs

Conflicts:
	src/mc/classic/worker.cc
Implement inhibitor arcs.

Handle the case where persistence is impossible.

In some cases (see example below), the persistence of a transition with an inhibitor arc is impossible.

tr t0 [0,1[ p0 p1?-1 ->
tr t1 [0,1[ p1 ->
pl p0 (1)
pl p1 (1)
net buffer

Don't support different types of arcs between a place and a transition.

Handle cases where both t and u arcs are inhibitors.

Extract the firing rule in a new file.

Code cleanup.

Check newly enabled before persistence.