Allow looking up component code from trace

[jonnor]

Would require the trace to either:

• Have code of all components included (very large, and won't work for non-component things included by component)
• Have enough info to know which component versions where, and how to look up the info. For node.js, this could based on a npm list dump, though maybe one should extract repo (typically but not alway github) from the package.json right away. Then would have to get the path from base of repo to the particular component. And have a way to HTTP GET the actual source code..

Since we want this in a non-NPM specific manner in general, there are some relationships here to noflo/noflo#247