GroupGraph: first attempt at a button to split selected nodes into axon and dendrite.
GroupGraph: generalized split arbor, to enable future modes
Arbor.js: new function simplify, to create topologically accurate
but simpler versions of the arbor, preserving a given set of nodes
as well as any relevant branch nodes in between.
SynapseClustering: new function to retrieve clusters as maps rather than arrays.
GroupGraph: new button to split by synapse clustering.

Now one or more selected nodes can be given a specific bandwidth value.

Splitting occurs in the client.
GroupGraph: on refresh, preserve additional text in labels of split nodes.

Still fails for branch nodes: they get recreated with text.
WindowMaker: help text for new tab of GroupGraph.
GroupGraph: removed obsolete properties clustering_bandwith and confidence_threshold
GroupGraph: remove unused property syncount
Merge branch 'gg-client-splits'