Making shape function work on cyclic graphs requires tracking the current graph level, which wasn't done correctly when this was implemented. Done properly now so going up and down on graph works as it did before.
Merge internal and external filtering in a single loop (solve problems caused by order of filtering)
Made graph length calculations work on cyclic graphs (it unrolls them)
Retag subgraphs when merging, to prevent loops
Mark missing up link in multi resolution as NULL
Ignore hidden vertices when propagating weight between islands
Axial symmetry tagging was depending on the order of the nodes, so it might tag left side as right and vice versa depending on the order. Stability test ensures the tagging is order independant (what it tags as right and left might not be the real right and left, but at least they are consistant between mesh graph and armature graph, so it doesn't flip limbs)
Also, setting the merge limit to be non-zero for armature graphs (since very small yet non-zero differences would prevent merges and correct graph creation)
