For PrestaShop 1.7.5.x

fix #37 #31 : fix footer responsive
add cart loading when edit product line cart
add loading spinner when add to cart
refacto modal add to cart (responsive)
sticky bottom for modal add to cart buttons (on mobile)
fix btn add to cart small width
add spinner loading for img placeholder loading
fix #36: fix microdata : rm inline microdata, use jsonld
fix override tpl viewed products
#44 slider auto transition
no use material icon from gg & edit gulp file
footer container margin top
fix #34
move offcanvas modal from footer to prevent css styling conflict
fix canonical (1.7.5 provide a new canonical)
fix #35
fix #29
fix #41
refacto cart-detailed-product-line.tpl (better responsive)
update boostrap 4.3.1
add gulpfile for fast compile scss (only for dev work)