R1:e2ed52735387

Add a very simple `bin/policy` script for CLI policy administration

Summary:
Ref T603. I want to provide at least a basic CLI tool for fixing policy problems, since there are various ways users can lock themselves out of objects right now. Although I imagine we'll solve most of them in the application eventually, having a workaround in the meantime will probably make support a lot easier.

This implements `bin/policy show <object>`, which shows an object's policy settings. In a future diff, I'll implement…