Update to FontAwesome 7

[lynnfaraday]

See #582 for a starting point.

Considerations:

1. The IconDefinition import moved, which is a breaking change requiring a major version bump.
2. Some of the icons changed slightly in appearance, so we should review known uses to ensure they're still appropriate.
3. We probably want to create our own Icon component rather than surfacing the FA IconDefinition, to insulate consumers of MDHUI from future FA changes.

See the other PR for more details/discussion.