Circuit export as CSV, TSV, XSV

[stewdio]

Add ability to export circuits as comma-separated values, tab-separated values, and a meta routine for arbitrary-character-separated values.

Once this is functional, add a button to the circuit editor for downloading the circuit in these formats.

Then need the converse; the ability to ingest a circuit from CSV, TSV, XSV, and the ability to drop such a file on to a circuit editor and have it respond accordingly. (Also include ability to drop a text file on to a circuit editor and ingest using the Circuit.fromText routine.)