Allows users to leave a project/group
that they have been added to.
Add function to leave a namespace by url param
If the `leave` param is present on a project/group show page,
click the leave link.
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
