Fix stale site icons.

Fix artist URLs still showing old cached site icons because the URL
didn't change when the file was updated. Use `image_pack_tag` so that
the filename includes the hash, so that the URL changes when the file
changes.

app/javascript/packs/application.js

@@ -14,6 +14,8 @@ import morphdom from 'morphdom';
 // should start looking for nodejs replacements
 importAll(require.context('../vendor', true, /\.js$/));
 
+require.context("../../../public/images", true);
+
 import jQuery from 'jquery';
 require("jquery-ui/ui/widgets/autocomplete");
 require("jquery-ui/ui/widgets/button");