[ImgBot] Optimize images

*Total -- 3,886.24kb -> 3,329.06kb (14.34%)

/doc/Visualizations/Stack/SmothDoubletsStack.png -- 874.85kb -> 516.66kb (40.94%)
/doc/TheoriesComparison/links_theory_3_links.svg -- 16.77kb -> 11.40kb (32.01%)
/doc/Math/Links_Set_Cartesian_Product.svg -- 22.39kb -> 15.35kb (31.46%)
/doc/Math/Links_Set_Cartesian_Product_Selected.svg -- 22.82kb -> 15.73kb (31.09%)
/doc/TheoriesComparison/links_theory.svg -- 17.08kb -> 12.03kb (29.58%)
/doc/TheoriesComparison/links_theory_3_links.png -- 22.81kb -> 18.25kb (19.99%)
/doc/Math/Links_Set_Cartesian_Product.png -- 136.34kb -> 113.09kb (17.05%)
/doc/Math/Links_Set_Cartesian_Product_Selected.png -- 136.70kb -> 117.05kb (14.37%)
/doc/Visualizations/Stack/3283_001.jpg -- 1,959.18kb -> 1,833.62kb (6.41%)
/doc/Visualizations/Stack/DoubletsStack.svg -- 677.29kb -> 675.89kb (0.21%)

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