Fix AFPSOFT-22 according to Scott Snyder suggestion.

Moved initialisation and definition of static const class members to
source files, becuase anyway the variables would have to be defined in
source files if they are ever bound to a reference. Lack of definition
can cause link failures, but often only in debug builds. See
<https://stackoverflow.com/questions/5391973/undefined-reference-to-static-const-int>