Create an Elefant app/theme directory and make the installer use that for easy browsing/selection

The directory would provide a simple read-only API to list the apps, and fetch their details including their preferred install option (url, github link, etc). This would be enough to build an app browser with an install button for any app or theme. This is much easier than pasting the URL or Github link manually into the installer.

Over time, this could be extended to include a ratings/reviews, demo and documentation links, and additional apps could be made to provide additional capabilities such as publishing your own apps and themes to the directory.