Debugger: Remove needless explicit copy constructors.

These worked in identical fashion to what the default copy
constructors would be, but their mere presence marks the class
as being "non-trivially copyable," which means that memcpy'ing
it is now a -Werror on GCC 8.

We have to be careful when making this change, though: classes
which *are* trivially copyable can be passed inside registers
on x86_64, so changes like these break ABI in a dangerous way.
These classes is private, so it should not be a problem, but
for other classes (e.g. BRect, BPoint) we cannot fix them
properly right now.

Debugger: Split into core library and application.

- Add subfolder src/kits/debugger which contains the debugger's core
functionality and lower layers. Correspondingly add headers/private/debugger
for shared headers to be used by clients such as the Debugger application
and eventual remote_debug_server. Adjust various files to account for
differences as a result of the split and moves.
- Add libdebugger.so to minimal Jamfile.