Started on an automated assembly step generator

[jmwright]

This is an attempt to generate assembly step CAD models/assemblies using the device ID from devices.json. The code generates a placeholder device based on the dimensions in the database, generates the matching shelf, then attempts to put them together.

There is still missing data in the database to make this fully automated. For instance, where are the mounting hole locations in the hardware, if there are any? There needs to be some way to know if there are screws involved, and if so, where they go.

[julianstirling]

I know this is a draft, but I am going to push forward and merge as:

• This is clear progress
• Lots of things are half finished in master right now
• I don't want to break everything when we do the split talked about in https://github.com/Wakoma/docs/issues/30