R1:814b586f5d3d

Add a "Description" field to Spaces

Summary:
Ref T8377.

- Add a description field.
- Add edges so files can be attached.

Test Plan: {F492410}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8377

Differential Revision: https://secure.phabricator.com/D13235