Updated coding style.

I'm always learning.
Containers: use noexcept only for constructors and destructors.
Containers: deinline heavy functions, remove redundant `inline`.

Constexpr functions and functions fully defined in class body are
always inline. I'm always learning new stuff. Also publicize deleted
functions so they show up in docs and `const`ed some variables.
Interconnect: inline/virtual optimization.

Deinlined heavy functions, removed redundant `inline`, changed virtual
destructor to protected nonvirtual. Also publicized deleted functions
so they show up in documentation.
PluginManager: inline/virtual optimizations.

Deinlined heavy functions, removed redundant `inline`, made
AbstractManager virtual destructor protected nonvirtual, as nobody
will ever need to delete AbstractManager* directly (hopefully).
TestSuite: deinlined heavy functions, removed redundant `inline`.
Utility: deinlined heavy functions, removed redundant `inline`.

Also moving strings instead of copying on a few places. All previous
cleanup commits shortened compilation time by ~10 seconds (~2:41
before, ~2:23 now).