This PR is for learning purposes only. I known it is incomplete considering some code standards, and there are margin for customization with better UI (for example, allow different minimum surface size). It examplifies how to create a new marker detector type that is used to detect a computer screen as a surface (potentially, any rigid brighter trapezoid surface in regard to the background).

• The new type creates markers from trapezoid corners detected from the biggest one at the field of view.

• Orientation is obtained by sorting corners with pre-defined assumptions and will always return top-to-bottom surface in regard to the world view (it is agnostic about head pose or real corner orientation). For stationary setups, it is not a problem at all.

• For stationary setups, I found it to be cleaner (no visual markers at all needed) and a lot more precise and stable than fiducial markers.