Adjust Sidebar changes

[foalsboy]

The PIPE team changed the approach a bit in a few of the areas we had in the sidebar, so we need to adjust the design of these changes.

1. App shell – Side bar, @sans-harness added “User management” menu item

2. Manage navigation popup (@praneshg239), new icons added

Pixel Point will come up with an updated design for these things soon.

[foalsboy]

Design updates:

Manage navigation (link), User Management in sidebar (link)

We'll pick this up soon

[abhinavrastogi-harness]

I remember there was some discussion to allow all items to be movable. That would mean we dont need to solve for point 2 here. We can just remove the check which prevents Repos and Pipelines from moving. Then we don't need custom icons for those either. We'll just show the standard drag-handles.
cc @c-joetaylor-harness