May be issue with saving graph, graph_load_test.yml especially.

Made output and preview nodes more hardcoded, don't delete them across clearNodes and loadGraph- this isn't working fully yet still.
Using keys in 'Mouse' now.  Want to have attack and delay options on the key outputs, should that be handled in a different (AttackDelay) node?
Made attack-decay-sustain-release node for turning binary signals (like keypresses from Mouse/Input) into more analog ones.  I'm not sure if the decay/sustain stage is really necessary, but it is easy enough to bypass with the right parameters.  Definitely some alternate approaches to produce s-curves instead of linear ramps would be nice.
SigToInd port is mux-like, it takes n inputs and outputs the index of the latest on to change to a positive number.  Very useful for connecting a bunch of keys to select the input from a real Mux or MuxBuffer.  Also some fixes for the SigADSR.
Create a browse dir node if the current input port is a dir
also create BrowseDir nodes for graph file and other file ports