[DS-1738] Support NUMERIC columns in database query result sets.

NUMERIC and DECIMAL results are now converted to BigDecimal, not
Integer resp. Long.
Hi @mwoodiupui , not sure I fully understand the Unit Tests, as it looks like you always set "instance" to null just before using it. Won't this continually throw an NPE?

Also, it looks like this PR is currently unmergeable as-is, which makes it harder to test out.