Added GraphicsContext() constructor that takes an existing, valid OpenGL context. This can be used for interop with third-party toolkits which create the OpenGL context themselves.
Improved CreateDummyContext logic to detect and use the context handle of the current thread or a specified handle.
Removed GetCurrentContext() methods from platform-specific context implementations (everything now goes through the relevant IPlatformFactories).
Added OpenGL 3.0 support for GLX contexts.
Added support for creating dummy contexts (useful if you are creating contexts from an external library).
Cleaned up unused and stale code.