Glowing highlight

I’ve just replaced the old construction highlighting (line drawn bounding boxes) with a new glowing outline effect.  When a construction is selected it glows blue.  Then, when aligning it to another construction, the colour changes to green if the attachment is valid, red if not (i.e. if parts are interpenetrating).  Constructions also glow blue when they’re frozen.

More UI / visualisation improvements coming soon hopefully…