ComputationHandler and GeospaceHandler

This change adds the concept of a ComputationHandler, designed to perform computations for computed columns from one or more source columns during ingress / upserts.   It also adds a handler for Geospace / geo region coding of point columns that are ingressed.
And note that it isn't just that it "should" be lazy, but it must be... if it isn't then it will blow up soda fountain OOM on large upserts.