Improve swh-web design for mobile browsing

While swh-web frontend is based on bootstrap for reponsive design, browsing the webapp on a mobile device is not really optimal.

For instance, directory views could be improved to get a look and feel on mobile similar to what GitHub or GitLab offers.

Migrated from T1477 (view on Phabricator)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information