New E_WINDOWPOS event when SDL notifies window movement. Support for setting initial window position beforecreation.
Engine: New WindowPositionX/Y init params. Sets initial window position prior to SetMode that creates the window.
Input: Notify Graphics subsystem about SDL window moved event.
E_WINDOWPOS and initial window position OGLGraphics implementation.
Use SDL_WINDOWPOS_UNDEFINED as the default window position to simplify code.
Added contributor credit.