R1:9160da1afb62

Add a Packages application and PackagePublisher

Summary:
Ref T8116. Partially scavenged from D14152. This roughs in a new Packages application for Arcanist extensions and third-party applications, and adds a "Publisher" object.

A "Publisher" represents an individual or entity who is publishing a package, like "Phacility". It's explicitly //not// necessarily the original author -- just the primary entity vouching for the safety of the code.

A publisher just has a name and a unique key for now. For…