Add lazy native attribute to images to avoid loading when hidden

[NeOMakinG]

Questions	Answers
Description?	On PS Dashboard, images were loaded even if they were hidden, adding this attribute permit to load images only when the module is shown
Type?	improvement
BC breaks?	no
Deprecations?	no
How to test?	Go on the PS dashboard (every version) with this module, open network tab when you load the page (on chrome especially), you shouldn't see some images like 8_1.png coming from the gamification module, and when you click on the trophy icon, you should see some images loading !

[Progi1984]

Thanks @NeOMakinG & @sarahdib