Upgrade to Polymer 3

[jadjoubran]

Since polymer 3 is now available That would let us get rid of bower 🎉

• [ ] Upgrade to Polymer 3
• [ ] fix webdash serve to emulate --module-resolution=node from polymer serve --module-resolution=node
• [ ] add import "/node_modules/web-animations-js/web-animations-next-lite.min.js"?
• [ ] Extensive testing
• [ ] Plugins?
• [ ] remove all bower related stuff
• [ ] removed package.json files hack from plugins since bower is not required anymore
• [ ] Update create plugin guide

[jadjoubran]

https://www.polymer-project.org/3.0/docs/upgrade