Common: Remove 'singleton maker'

I already stated that I despise singletons, and I see no reason why
should I make exceptions.

I think, that static members would serve better for this purpose,
for example

	class ILogger {
		static ILogger* globalLogger_;
	public:
		static void setGlobalLogger(ILogger* logger);
		static ILogger* getGlobalLogger();
	}
Core: Remove getSettingsManager()

See e2f3fb56d2e43841ebd5f808122aafed49831aa0 for rationale.
/CGame.cpp