Add quick size references

[Pullusb]

Optional / Bonus feature

Since we are in a 3D environment where it is preferable to use real world scale models and drawing. It might be interesting to have some sensible scale references.

Useless the board is purely 2D

This can happen multiple ways:

• Add quick 3D reference basic object (human, car, door, chair, bench)
• Add 2d lines, or GP showing human scale (can be directly on drawing object, openGL overlay on grid respecting drawing orientation?)