Add VerticalSync option to WindowManager

[jvyden]

• Renames WindowManager.UpdateFramerates() (private) to WindowManager.UpdateGameView() to reflect new functionality
• When unfocused, VSync will be disabled. This is because VSync enforces a higher fps when enabled; disabling it when unfocused will allow us to retain the TargetUnfocusedFramerate.
• VSync is managed through WindowManager.VerticalSync.

This is useful for applications that do not require high framerates and low latency; instead low-power ones that only need to hit the monitor's refresh rate.

[jvyden]

By the way, if needed I can add a test for this in Furball.Game.

[Beyley]

Could you add a config option in furball too?

[jvyden]

Sure.