Phortune v0.1: products

Summary:
Ref T2787. A product is the abstract representation of something you can buy or rent/subscribe to. Although the interface isn't locked down yet, this would ultimately be internal/administrative.

Products likely have some user-facing skin on top of them: plans would have a purchasing/comparison flow, physical goods would have a storefront, etc., so products don't have any information like descriptions or images, just the data that Phortune needs to correctly bill accounts.

Generally, this is very basic for the moment.

Test Plan:
{F37594}
{F37595}
{F37596}

Reviewers: chad, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2787

Differential Revision: https://secure.phabricator.com/D5441