R1:a1df1f2b7041

Allow projects to be set as policies

Summary:
- Renames `PhabricatorPolicyQuery` to `PhabricatorPolicyAwareQuery` (a query which respects policy settings).
- Introduces `PhabricatorPolicyQuery`, which loads available policies (e.g., "member of project X").
- Introduces `PhabricatorPolicy`, which describes a policy.
- Allows projects to be set as policies.
- Allows Paste policies to be edited.
- Covers crazy cases where you make projects depend on themselves or each other because you are a…