Debugger: Add dedicated functions for global {un}init.
- Add new source file DebuggerGlobals, which contains the relevant
functions for initializing/destroying the various singleton rosters
that the core subsystems rely upon. It is the app's responsibility
to ensure these are called before anything else, and as final cleanup
at exit.
- The GUI/CLI app objects now take care of initializing the settings factory
and ValueHandlerRoster, as those are entirely app-specific.
- Refactor calls to init functions appropriately.