Implement new UI component for icons #230

- Introduce `AppIcon.vue`, offering improved performance over the
  previous `fort-awesome` dependency. This implementation reduces bundle
  size by 67.31KB (tested for web using `npm run build -- --mode prod`).
- Migrate Font Awesome 5 icons to Font Awesome 6.

This commit facilitates migration to Vue 3.0 (#230) and ensures no Vue
component remains tightly bound to a specific Vue version, enhancing
code portability.

Font Awesome license is not included because Font Awesome revokes its
right:

> "Attribution is no longer required as of Font Awesome 3.0"
>
> Sources:
>
> - https://fontawesome.com/v4/license/ (archived: https://web.archive.org/web/20231003213441/https://fontawesome.com/v4/license/, https://archive.ph/Yy9j5)
> - https://github.com/FortAwesome/Font-Awesome/wiki (archived: https://web.archive.org/web/20231003214646/https://github.com/FortAwesome/Font-Awesome/wiki, https://archive.ph/C6sXv)

This commit removes following third-party production dependencies:

- `@fortawesome/vue-fontawesome`
- `@fortawesome/free-solid-svg-icons`
- `@fortawesome/free-regular-svg-icons`
- `@fortawesome/free-brands-svg-icons`
- `@fortawesome/fontawesome-svg-core`

package.json

@@ -35,11 +35,6 @@
   },
   "dependencies": {
     "@floating-ui/vue": "^1.0.2",
-    "@fortawesome/fontawesome-svg-core": "^6.4.0",
-    "@fortawesome/free-brands-svg-icons": "^6.4.0",
-    "@fortawesome/free-regular-svg-icons": "^6.4.0",
-    "@fortawesome/free-solid-svg-icons": "^6.4.0",
-    "@fortawesome/vue-fontawesome": "^2.0.9",
     "@juggle/resize-observer": "^3.4.0",
     "ace-builds": "^1.23.4",
     "cross-fetch": "^4.0.0",