Migrate UI to jaegertracing and to Apache license v.2

[yurishkuro]

Per jaegertracing/jaeger#409

• Move the repo
• Re-register the repo with Travis
• Re-register the repo with Coveralls/CodeCov
• Update the links to badges in the README
• Add DCO file
• Add sign-off checker bot
• Update CONTRIBUTING instructions to require sign-off
• Update to Apache license
  • Replace LICENSE file
  • Update CONTRIBUTING instructions and references to license in the README
  • Update the existing license headers (keep Uber copyright)
  • Update the check-license script (new files get The Jaeger Authors copyright)