Simplify and centralize configuration loading mechanisms

[jvyden]

• Allows tests to easily generate empty configs. Prevents them from using filesystem configs entirely.
• Configuration loading is behind a lock now. This nullifies the weird random failures caused by unit tests generating config files but doesn't actually serve too much purpose as the codepath isn't hit by unit tests anymore. Kept as it shouldn't technically harm anything.
• Reduces the complexity of config management in RefreshGameServer and TestRefreshGameServer
• Allows the new Refresh.WorkerManager server to easily utilize all the configs from the main GameServer project