Handling GUI event such as window resize, window closed

[bennylp]

While in general there are only few window events to be exported to application, since video window has no decoration (hence user cannot move, resize, close, etc.), there are events that may be interesting to app:

• if incoming video format/size has changed, and video window is updated. App needs this to move/resize the window to fit the app window.
• mouse click to video area may be interesting to app