working on pruning the tree [not executable]

It doesn't work right now, but i thought i'd make a commit now anyway -
in case i throw the current concept over board it'll be nice to have
these funny (terribly non-optimized) code-pieces from TreeBuilder in the
repo at least in this commit :)
NodeClusters are saving the duplicate nodes and then i let each cluster
merge into a single node from the bottom upwards in the end. But
something along the line is messed up, i don't get a working graphml
export...
Thinking about a different concept implementing a node-storage that is
always sorted, it adds new node at the right place and thus can always
tell how many duplicates a node has.
OR avoiding duplicates alltogether by computing the nodes first (by
saying for instance, which set of uniquely different configruations can
i create with 5 empty fields and 2 marks of type A and 2 marks of type
B) and then looking where to attach them by asking from which node could
i get to this configuration in one move... yeah, let's see. I might even
use Excel to figure out the scheme for the latter.