Use client-side routing in Beverage Buddy

[vlukashov]

When showing how client-side bootstrapping works in Vaadin 15+, I want to have a version of the Beverage Buddy starter that uses client-side routing, so that I can show a demo application that compiles and runs using this feature.

DoD:

• update the ccdm branch in the beverage buddy repo
• change routing from server-side (V14) to client-side (V15+)
  • add a client-side parent layout
  • replace the server-side 'categories' view with a client side equivalent view based on LitElement, with hard-coded dummy data
  • use the flow.navigate method to fall back to server-side navigation
• do not use Connect to get the data from the server-side, use hard-coded data