Modernize LoKiCore

• replace Convertible.h with std::is_convertible
• do not compare pointers to 0, prefer nullptr over 0
• add move constructor to BiFunction's FunctorFromFunctor
• use copy-and-swap in BiFunctions's FunctorFromFunctor operator= and copy c'tor
• add final when oppropriate
• do not explicitly specify trivial destructors
• prefer STL algorithms
• generalize and simplify Apply
• add SFINAE-constrained perfect forwarding in Math.h
• implement Not and Negate as special case of UnaryOp
• use override instead of virtual when appropriate
• remove obsolete SVN keywords
• add a Streamer operator>> for rvalues input