Proxy web requests through a node express backend

This change allows proxying API calls to the bgd-server through a node-express backend. This is especially useful for backend systems that use http, but their domains are configured with HSTS browser settings. These settings cause browser based calls to the services to be upgraded to https, causing them to not function.

With this change, all API calls are being proxied through the node express application, meaning there is no HSTS concern. It also enables adding https to the bdg-browser independently of the servers.