Add SQL for column adding

[mathemancer]

Related to #2737

This adds some well-tested SQL functions that let you add columns to already-existing tables.

Technical details

These functions are not yet used in the Python layer as of this PR, in order to scope things. Only functions which are intended to be used from Python are directly tested.

Screenshots

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[dmos62]

Looks good. I didn't review 0_msar.ql very thoroughly, but the tests look good so I'm comfortable.