Fix MultimeterBase export. Update example to use DMM

A missing module.exports was preventing DMM-based circuits
from loading.
Add removeComponent to external API

Note that the `sparks` object is the only world-facing object in
the library, so anything that an outside library wants to use must
be added to that API.

In this case, the current teaching-teamwork demo uses 'removeComponent'.
Add workbenchController to API
Delay require of workbenchController, due to circ dependency
Allow components to define themselves as hidden