WIP: Use Vuex+Vue+new API for Job log page

What does this MR do?

TODO's

• Create main Job app
  • Delete old header component, use ci_header directly
  • Remove mediator
  • Remove service
  • Remove loading icon from sidebar
  • Update sidebar HTML to match haml
• Handle Scroll behavior
  • Automatically scrolls to bottom after trace is loaded
  • Scroll down button shows animation while automatic scroll is active
  • While log is not complete, if user hasn't scrolled, keep scrolling to the bottom every time we receive more log
  • Stop scrolling down automatically after user has scrolled once
• Make scroll behavior reusable in master so we can use it here: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21931
• Top bar needs affix
• Handle component's adjustments to match the API https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21930
• Empty states illustrations path need to be updated on BE to work with Vue
• Scroll down animation svg is not working in vue because the icon is not the same and classes are now dynamic.
• Missing has_trace check: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21950
• Sidebar collapse behavior
• Fetch stages from pipeline.path
• Fetch stages content from pipeline.path/stage.json?stage=$STAGENAME&retried=1

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides

Closes #50904 (closed)