moving constructors/prototypes into their own files (true modularity can come later)
added data and updated pipeline constructor to take data types
workflow view now can show pipelines that only span part of a workflow (still doesn't show rings for pipelines with just one data type)
code reorganization
still not drawing pipeline circles...
prevent outbound paths of a node edge from overlapping when the destination nodes are on different ranks
pipeline circles showing up, but need to position/size correctly and attach events
before refactoring graph_drawing.js
idiomatized d3 code