Add new macros wxDECLARE_DYNAMIC_CLASS_NO_ASSIGN_DEF_COPY() and
wxDECLARE_NO_ASSIGN_DEF_COPY() and use them instead of
wxDECLARE_DYNAMIC_CLASS_NO_ASSIGN() and wxDECLARE_NO_ASSIGN_CLASS()
respectively to ensure that we declare a (default, if possible) copy
ctor in the classes declaring an assignment operator to avoid clang
warnings about not doing it.