Link together the angular and flask sides

First step of solving #23.

Frontend tests and scripts will need to be adjusted to match the new structure, but for now a full end-to-end app (that lists open features) can be browsed at http://localhost:5000/

Another pending thing is to ~~serve the homepage on `/` from a flask view, and~~ turn the static `index*.html` into proper jinja templates in `templates`.