Arvados » Arvados Workbench 2

As an admin, I would like to have the possibility to mark content as "Public favorites",
so that, it will appear in "Public favorites" section and will be visible for all users.

Acceptance criteria (Public Favorites - PF):
- only admins can mark content as "Public favorites".
- action available in: more options icon, by right click
- the new section should be available in the search interface and in file selection during running a process
- an end user is ALLOWED to: copy content from PF, copy to Projects inside PF (not directly to PF), use content from PF to run a process, edit content in PF
- an end user is NOT ALLOWED to: copy directly to PF, add content to PF, remove content from PF

Mockup: https://3czrf1.axshare.com/#g=1&p=14__public_favorite&c=1

https://dev.arvados.org/projects/arvados/wiki/Cluster-wide_favorites