Figure out how to deal with packaging image assets for publishing

raw.githubusercontent.com could be an option
Looks like from this to using CDNs (`jsDelivr`, `unpkg`), the shared starting point is to make a separate repo under jspsych organization that is just for assets? Then the asset can be downloaded during runtime from the CDN URL. The trade-off for this is need to maintain a separate assets repo that is organized to parallel timelines