reverse engineering library setup from slider

https://work.montagestudio.com/app/5a2ed9b28a30fe67da6739522fc1837e6108e21a/extensions/digit.filament-extension/library-items/digit/slider.library-item/slider.html

for https://github.com/ProjetDeRechercheSurLecriture/DyslexDisorthGame/issues/158
Adding blank image to avoid black box
checking in bower components to simplify install
using webfonts instead of local font to simplify install
found a this
using https
making experiment report have black text
customizing digit image to handle black squares

for https://github.com/ProjetDeRechercheSurLecriture/DyslexDisorthGame/issues/148
Merge pull request #1 from ProjetDeRechercheSurLecriture/master

Adding logic to check if images exist before displaying them