Icon preview in local server & docs for Community App Catalog

We need a way to display icons for testing for catalog submissions. Also documentation for how to do it.

Horizon Plugin Packages for Community App Catalog

We need to figure out how to get a release of a tarball, a pip package, an rpm, and a deb.

Tighten Schema for Community App Catalog

Each of the asset types have some similar things that have very different schema's. Make them more uniform and tighten the allowed fields for v1 schema.