ConfigUtility now supports recursion; is a Singleton

If you have "config.next" set, the config system will load that as another
config file. Higher config files have a higher precedence over subfiles
when conflicting keys are encountered.

* Added singleton.hpp, containing Singleton<T>
* ConfigUtility now inherits from Singleton
* Tweaked timer.*pp layouts
Implemented the changes to ConfigUtility in the client and server

The server's changes were easy. The clients means that the constructors
for each scene have one less argument, and each scene has one less member.
The exception to this is LobbyMenu, where the config is used in multiple
places, so it was easier to have the config's reference as a member.

To replace the config's usage, I added this line in most cases:

ConfigUtility& config = ConfigUtility::GetSingleton();

The only requirement is that ConfigUtility::Create() and
ConfigUtility::Delete() are called from the main() function.