Completely remove dependency on MementoEmbed instance JavaScript for MementoEmbed cards

[shawnmjones]

By default, MementoEmbed cards require JavaScript that is hosted with a MementoEmbed instance. If that instance goes away, the cards degrade.

We have two options:

1. host the JavaScript somewhere more permanent, like a web archive, a CDN, or GitHub Pages
2. remove it entirely and hard code everything the JavaScript would have done -- this is already available via the API

If we go with number 1, we can make smaller embeds. If we go with number 2, the embeds will be larger but impervious to degradation.