Define transformation algebra outside of Python

[nsbgn]

This is not something that should be addressed anytime soon, but eventually it might be nice to define transformation algebras not as Python Language objects but read them from RDF files. Something like:

lang:type [ a lang:Set, :params 1 ], [ a lang:Int ].
lang:operator [ a lang:sum, :type "Set(Int) -> Int" ].

This way, we would become more implementation-independent.