browse: Add panel for swh persistent ids display

This commits adds a popover panel reachable from the 'Show identifiers'
entry in the 'Actions' menu for displaying swh persistent identifiers
related to the currently browsed objects (content/directory/release/
revision + snapshot context if any).

The panel offers easy copy to clipboard of the swh ids and related
urls but also the possibility to add optional parts (origin info
for instance).

Closes T1004