w3admin billing enhancements

[travis]

What
The w3admin tool already shows some billing-related information - we should consider adding Stripe usage, space diffs, space snapshots and allocations to the UX in some form or another.

Why
w3admin is a useful tool for understanding the state of accounts in our system and we should update it as our user management needs expand

Cost
I think we could get some additional information pretty quickly, but I think a full pass on this would require 3-4 days of work as it's likely to require additional API endpoints.