Tooling common UI: Move source from third parties to external-src
- Consistent with rest of code base
- Allows “warnings removal builder” to do its job
(from redmine: issue id 3217, created on 2017-12-06, closed on 2017-12-06)
(from redmine: issue id 3217, created on 2017-12-06, closed on 2017-12-06)