Default or delete most constructors/assignment operators

[ZedThree]

See following C++ Core Guidelines for rationale:

• https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c20-if-you-can-avoid-defining-default-operations-do
• https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c21-if-you-define-or-delete-any-copy-move-or-destructor-function-define-or-delete-them-all

Basically we can rely on the compiler to generate all of these for us. This PR is net -400 lines and does exactly the same thing.