[WIP] Create ElectrodeTable type

[rly]

Motivation

Requires the electrodes_table schema branch. Hold for new schema release.

Testing not complete yet. Stashing changes publicly here.

How to test the behavior?

Show how to reproduce the new behavior (can be a bug fix or a new feature)

Checklist

• Did you update CHANGELOG.md with your changes?
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[stephprince]

I believe this PR can be closed since it was superseded by #1890 which has since been merged.