_tree_header.html.haml

Continues the iteration on the project overview UI:

- moved star, fork and new clone button
(copy SSH/HTTPS URLs) to top right,
  made them smaller
- avatar is now larger (64px)
- 'Request access' is now a link instead
  of a button
- overview comes before the description +
  changed styling and added icons
- description font-size is now 16px (large-paragraph)
- quick links to files are moved downwards
  below the commit/pipeline info
- margins changed to group content into
  4 groups to clean up the interface
- visibility info reduced to icon-only and
  moved to the right of the title