migrate to "serverless"

[gassc]

I think with a hosted AGOL resource proxy, I can drop the Flask portion of this application and still use Esri premium services for the watershed and elevation profile fallback. That would vastly simplify builds, deployment, and hosting (I could even run it from a gh-pages branch here).

It would require:

• a bit of work to migrate from the Flask application structure and jinja2 templates to a Jekyll structure with liquid templates.
• some slight changes the javascript to remove token handling