Add custom field storage to Projects

Summary: Ref T4010. Adds storage and indexes for custom fields. These tables are the same as people/maniphest/differential.

Test Plan: Ran `bin/storage upgrade`.

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Maniphest Tasks: T4010

Differential Revision: https://secure.phabricator.com/D7369