Add post-voting message box

Add a message box that displays after voting, below the vote button.

This adds a showVotedMessage data item that's set by checking for a sessionStorage value. That value gets set when redirecting after saving a vote, and then removed when the banner is displayed.

The container element is also changed here, because it was being set to the parent of .community-wishlist-voting-btn which was an <a> and we don't want to go sticking the message div inside that (and it's just generally nicer to have the app be inside a generic higher-level div).

Bug: T363231