Remove MiniCart dependency

MiniCart has grown apart from JSButtons, so I propose we remove it as a dependency of JSButtons.  Users can still use MiniCart in conjunction with JSButtons.  I'll continue to keep the buttons w/ minicart bundled file up on the CDN, but won't mention it in the docs anymore.

#101 should be merged afterwards (contains gh-pages changes)

- [ ] Reviewed by @jeffharrell