Change name of nested struct to avoid name clash with member function

The persistent class reco::SoftLeptonProperties has a nested struct named "quality", and also member functions named "quality".  Although this is legal C++ (although poor style), it confuses the dictionary generation of ROOT6, which produces a dictionary that will not compile.  Although ROOT6 should fix this problem (a ticket will be written against ROOT6), we can easily avoid the problem by giving the nested struct a distinct name from the member functions.  This pull request renames the nested struct from "quality" to "Quality".
This avoids poor C++ style, avoids a ROOT 6 problem, and also makes the code more compliant with the CMS practice of naming classes and structs beginning with a capital letter.
Tested with git cms-checkdeps -a and the relval matrix.