Hierarchical navigation using breadcrumbs (pypi#12315)

* Uniform spacing for every .badge class

- `margin-left: 0.5em` to add space between text and badge.
- `vertical-align: 0.15em` to align badge to middle of parent.

* NFC: Remove obsolete *badge classes

- .organization-snippet__badge
- .package-snippet__badge
- .release__version-badge

* Add {Projects,People,Teams} count to org menu

* Add {Projects,Members} count to team menu

* Add {Releases,Collaborators} count to project menu

* Use badges for counts in manage organization pages

* Use badges for counts in manage team pages

* Use badges for counts in manage project pages

* Use badges for counts for "Your organizations"

* Use badges for counts for "Your projects"

* Use badges for counts for "Pending invitations"

* Default to "Projects" when managing organization

* Default to "Projects" when managing team

* Use badges for counts for "{org} teams"

* Remove counts from headings in left side panes

- "Your projects"
- "Your organizations"
- "{org} teams"
- "{org} projects"

The counts after these headings ended up looking out of place.

* Adjust badge size according to parent's font size

- {`font-size: 0.8rem` => `font-size: 0.7em`}

* Fix space and underline after icons in badges

- Remove underline of space after Font Awesome icons in badges.
- Add more space after Font Awesome icons in badges.

* white-cubes.{png,svg}

* Switch icon for projects {cube => cubes}

* Adjust size and color of background icons

- sitemap.{png,svg}
- users.{png,svg}
- white-cubes.{png,svg}

Sharpened borders, increased contrast, and normalized size and position.

* Fix swapped PNG/SVG fallback in snippet background

* Adjust size and position of snippet background

* Breadcrumbs to manage project

* Use title with subtitle for release navigation

- "Releases" or "Yanked releases" as title
- "Version {{ version }}" as subtitle

* Breadcrumbs to manage organization

* Breadcrumbs to manage team

* Breadcrumbs to manage account

* Icons for breadcrumbs

* Larger .fa-cubes icons

.fa-cubes icons look smaller than it actually is. Balance out this
perceptual tendency by making .fa-cubes icons a bit bigger.

* Move {org,team,proj} name before breadcrumb icon

* Simplify breadcrumbs by removing last breadcrumb

The breadcrumbs were overly complicated. This should be better.

* Fix inconsistent icon for "Your organizations"

* Add breadcrumbs padding to align with side pane

* Remove duplicate item from mobile nav menu

* Fix inconsistent icon for "Your organizations"

Co-authored-by: Ee Durbin <ewdurbin@gmail.com>

warehouse/admin/templates/admin/base.html

@@ -100,7 +100,7 @@
         </li>
         <li>
           <a href="{{ request.route_path('admin.project.list') }}">
-            <i class="fa fa-cube"></i> <span>Projects</span>
+            <i class="fa fa-cubes"></i> <span>Projects</span>
           </a>
         </li>
         <li>