Bundle YUI and serve as asset

[hatched]

Fixes #3926 Fixes #3924

To QA

• For JAAS
• ./run and everything should work as normal. In the devtools you should only see a single yui-bundle.js instead of a number of yui js files.
• For Juju
• Bootstrap a new controller
• ./run exec yarn run build-prod-dist
• juju upgrade-gui <path to dist>
• The GUI should work as expected and have the same smaller asset list as above.