Add server-generated /config.js; add error boundary

Makefile

server/server.go

web/public/config.js

web/public/index.html

web/src/app/SubscriptionManager.js

web/src/app/config.js

web/src/app/utils.js

web/src/components/ActionBar.js

web/src/components/App.js

web/src/components/ErrorBoundary.js

web/src/components/Navigation.js

web/src/components/SubscribeDialog.js

web/src/components/hooks.js

web/src/components/routes.js