Property system: some simplifications and bugfixes

this simplifies the template meta programming a bit. (Which does not
mean that it suddenly gets easy.) The main motivation for this work is
to make the splices feature work properly which allows eWoms to
properly select the spatial discretization at any point.

Further, the number of type tags a node can inherit from now is truely
unlimited thanks the the generic tuple reversal class provided by
https://sydius.me/2011/07/reverse-tuple-in-c/ . (before, the maximum
number of nodes from which a type tag could inherit was 11, so this
limitation did not really matter in practice.)
Merge pull request #446 from andlaus/propertysystem_fixes

Property system: some simplifications and bugfixes