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

NUMERIC and DECIMAL results are now converted to BigDecimal, not
Integer resp. Long.
Notice that most of the tests are commented out.  I only wrote real tests for getNumericColumn and setColumn(String, BigDecimal).

Now rebased on much more recent code.  I had to move your Oracle magic from MockDatabaseManager into TableRow, which knows what is being done with these Integers and Longs and things.