refactor(icons): replace FontAwesome with Tabler Icons

Drop the three @fortawesome/* packages (v5, with a stagnant Vue 2
binding) in favor of @tabler/icons-webfont. The old <awe-icon>
wrapper is replaced by <vaquant-icon>, named after the project so
future icon-library swaps don't require another rename.

src/components/UserNew.vue

@@ -41,7 +41,7 @@
     </div>
     <div class="column is-1" v-if="!isMainUser">
       <button class="button is-danger" @click="$emit('remove')">
-        <awe-icon icon="trash" />
+        <vaquant-icon icon="trash" />
       </button>
     </div>
   </div>