Localize third-party JavaScript #20

Right now, the handful of third-party JavaScript dependencies is a mish-mash of files checked into the repo and links to CDN scripts. We should manage all that properly. Make the default to pull the dependences from NPM, install them as part of the build process, and maybe make using a CDN an option you can turn on.

This will have the nice side-effect of letting us upgrade TinyMCE, which currently requires an API key if you want to use the latest version from the CDN.