Use of boost::make_shared in parser

For classes lsst::qserv::parser::ModFactory
and lsst::qserv::parser::SelectFactory.
Some replacements couldn't be performed
for next reasons:
* lsst::qserv::parser::ModFactory::LimitH(
  const lsst::qserv::ModFactory&)
  lsst::qserv::parser::ModFactory::OrderByH(
  const lsst::qserv::ModFactory&)
  lsst::qserv::parser::ModFactory::GroupByH(
  const lsst::qserv::ModFactory&)
  lsst::qserv::parser::ModFactory::HavingH(
  const lsst::qserv::ModFactory&)
  do not exist.
* lsst::qserv::parser::SelectListFactory
  constructor is private