Switch to NPM import/build for NetlifyCMS

[eaton]

We want to add some extra CMS widgets, so we need to do some fancy things and build it ourselves. The NetlifyCMS site has instructions but our stripped-down site skeleton doesn't have any JS/SASS tooling yet.

Once we get that in place, we'll probably just need to change the /admin.index.html file to point to our custom built version of the file.

[eaton]

The critical bits (external storage of categories, generated UUIDs) are workin* using an external CDN and manual manipulation of the CMS object in the index file. Having the option of a full build still would be excellent, though.

[eaton]

May not be as critical as initially thought — got external widget plugins working the "simple" way with script tags in admin/index.html. What is potentially interesting is file-storage APIs for externally hosting the audio files. NetlifyCMS supports those as plugins just like widgets, but right now only supports "Cloudinary" and a couple of other paid providers. Not sure what straight S3 integration or support for Fission's storage APIs would look like, but it could be interesting.