Code modernization and cleanup contributions

[akleshchev]

Contribution by RyeMutt:

Replace boost noncopyable usage with modern c++ deleted operator #5076
Replace boost ptr_vector with std::vectorstd::unique_ptr which can also contain null pointers. #5073
Replace boost::hof::invocable with c++17 std::is_invocable #5071
Replace boost::assign usage with modern c++ brace initialization #5068
Remove dead llblowfish and llmail code plus related tests #5074
Remove dead experimental atmospherics code left over from EEP development #5070

Basically code modernization, cleanup and added safety.

Sadly no test plan. Consider changes to be code only. Ex: 'noncopyable' prevents programmers from accidentally accessing functions that should not be callsed.