Modernize FileStager
- make interfaces a struct, and inherit from extend_interfaces
- prefer range-based loops over BOOST_FOREACH
- prefer compiler generated destructors
- prefer (implicit) std::initializer_list over (explicit) boost::assign
- prefer Gaudi::Property over explicit declareProperty
- avoid snprintf if possible
- prefer std::unique_ptr over explicit new/delete
- prefer .emtpy() over .size()==0
- prefer nullptr over 0
- simplify arguments used for execvp (just point to contents of std::string)
- prefer auto
- add final qualifier
- prefer CommonMessaging