Update app and add npm start command

[leymannx]

Oh, I'ld like to see this app in action. But unfortunately with the current package.json I get a lot of deprecation notices and warnings on npm install. Also, nowaday an Electron app usually gets started with npm start. When I finally get the app to run with script/run I'm not able to do click anything. Canvas and toolbar is there but that's it :'(

[noisiak]

I also couldn't run the app (nor the curve.js library example).
Hope there is a workaround. This seems very cool.