Add glitch-lily as an installable frontend

As per @tusooa's recommendation in IRC, I'm adding glitch-lily as an installable frontend. This will allow instances that want to have a multi-column frontend akin to Mastodon's to do so more easily.

The only problem I'm encountering is the page rendering only the text "packs/index.html", which I don't know if it's due to how I set up or something else. This problem is fixed.