Add "standard library" of component models and associated mapping

[follower]

Initial plan is to make this from STL models already gathered for examples and also generated from the SketchUp models in the SparkFun repository (#17). (Which we could presumably push back to the SF repo.)

Once we have the models we need to create the mapping from component name to the model file path and integrate that.

[follower]

This is now here: https://github.com/Omniblox/pcb-component-models

The models still need QA for correct orientation etc.

[follower]

Current status:

• Need to commit/document tool scripts: update_model_repo.py, scan-brd-files.js
• Ongoing model QA.