Implement UI using Polymer

[ghost]

https://folio.googleplex.com/uproxydesign/uProxyAir/App

• [x] Loading and connected animations
• [ ] Delete server
• [ ] Server location
• [ ] Server strength

[trevj]

Loading and connected animations: https://github.com/uProxy/uproxy/pull/2850

[trevj]

TODO:

• server description (location)
• server "strength"
• delete server

[fortuna]

FYI, I added the list to Santi's issue description as a check list