Are you still having issues with Galleria?
I have used this plugin extensively.
A few important things:
In general, Galleria scripts need to be adjusted to work effectively in Shopify. More specifically, all image/icon references in the script need to be corrected to point to Shopify assets.
Let me know if you need any assistance outside of this.
You can use CDN without having to rewrite scripts - that way they mange folder structures that are otherwise not supported in Shopify assets directory.
<!-- load Galleria -->