colour detection

I've discovered another near-impossible weakness in QC - the ability to use a mouse cursor (or any coordinate) to select arbitrary objects. This can be done pretty easily in javascript if there are only a few objects that are the same size, but if they're all different sizes and there are many of them, it's very difficult to tackle.

This would probably be a prerequisite for the GUI widgets etc.

In a more general form, collision detection might be handy to solve this...