Review usages for numbers traits

[Mec-iS]

FloatNumber and RealNumber are used inconsistently as the latter is a compound of the former. Some methods accept one or the other, some both. They both works with PartialOrd. Need to figure out if we need both or if one can be dropped. Having a sort of UML graph for the modules could help spot where discrepancies are present.

This is a formal issue, in terms of implementation both are good to work with.