icephys - config for assembly

- micropipette
1. glass type (create enum) - what are the options here @gouwens (is it just glass type (borosilicate) or pipette(?) type (eg. borosilicate, OD 1.0, ID 0.5)? Is this too in the weeds?
2. internal solution (create enum of solution names, including OTHER)
We discussed having a solution class that can be used if OTHER. How would that work in here?
4. resistance (optional) decimal
5. resistance_unit default=MOhms(this might require a resistance unit to the units in models)

- manipulator coordinates
optional? Depth is the most important value.

-headstage gain
headstage gain unit - is this percent? @gouwens