ParserItem: improve the equallity testing code and remove the defaultSet() method

but we still need the m_defaultSet member because NaN == NaN as well
as NaN != NaN...
fixup! extend "StarToken" class and rename it to "RepetitionToken"
fixup! make the defaults of an item settable per data point
fixup! make ParserItems always defaultable
fixup! add some defaulted values to the unit test of PVTG