This commit introduces DataConvert UTs.
DataConvert::decimalToString now can negative values.
Next version for Row::toString(), applyMapping UT checks.
Row:equals() is now wide-DECIMAL aware.
Binary NULL magic now consists of a series of BINARYEMPTYROW-s + BINARYNULL
in the end.
ByteStream now has hexbyte alias.
Added ColumnCommand::getEmptyRowValue to support 16 byte EMPTY values.