2019 update and fix issues

## Issues
- Fix import not working when using Webpack #15 

## Code
- Use LitElement instead of Polymer
- Use open-wc/testing instead of WCT

## Development
- Improve serve (use Parcel bundler)
- Move style to a stylesheet file
- Add eslint config

## Release / CI
- Improve CI release config
- Include a bundled release