Proof of concept to add a visual coordinates grid#1

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didoo wants to merge 4 commits intomathieudutour:masterfrom

Commits on Apr 30, 2020

quick draft to add a visual coordinates grid (proof of concept for PR)
Cristiano Rastelli
committed

Commits on May 3, 2020

better grid in SVGViewer
Cristiano Rastelli
committed
improved code for grid generation (not final yet)
Cristiano Rastelli
committed
small improvements to the usage of the scaling factor
Cristiano Rastelli
committed