Migrate icons from Font Awesome to Material Design Icons

The Software Heritage Web application currently uses icons from the 4.7 release of Font Awesome. That release is quite old now (current upstream version is 5.13) and the set of free Font Awesome icons is not really exhaustive (a commit icon is missing for instance, so we use the one from github instead).

Another alternative free iconic font for the web is Material Design Icons : a growing icon collection allowing designers and developers targeting various platforms to download icons in the format, color and size they need for any project.

Material Design Icons collection is really exhaustive (no need to pay to get all icons as with Font Awesome) and open source. It is packaged under the SIL Open Font License 1.1 (same as Font Awesome).

So let's migrate swh-web icons to Material Design Icons to get consistent icons style and ease the integration of new ones in the future as the Web UI evolves.

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Migrated from T2445 (view on Phabricator)