Add feature flag for opening external links in a new tab (#749)

Closes https://github.com/modrinth/knossos/issues/438

components/ui/Modal.vue

@@ -3,7 +3,7 @@
     <div
       :class="{
         shown: shown,
-        noblur: !$orElse($store.state.cosmetics.advancedRendering, true),
+        noblur: !$orElse($cosmetics.advancedRendering, true),
       }"
       class="modal-overlay"
       @click="hide"