feat(addItemByTag): Always use lowercase tag

Resolves: #1

src/js/main.js

@@ -158,6 +158,8 @@ export async function addItemByTag(tag) {
     throw "Internal Error: Tag not length 6.";
   }
 
+  tag = tag.toLowerCase();
+
   console.log("Trying to add item by tag:", tag);
 
   var response = await fetch(config.backend_url + "/tag/" + tag, {