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 dastardly villan.

Test Plan: Set paste and project policies, including crazy policies like A -> B -> A, A -> A, etc.

Reviewers: vrana, btrahan

Reviewed By: vrana

CC: aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D3476

src/applications/project/query/PhabricatorProjectQuery.php

@@ -16,7 +16,8 @@
  * limitations under the License.
  */
 
-final class PhabricatorProjectQuery extends PhabricatorCursorPagedPolicyQuery {
+final class PhabricatorProjectQuery
+  extends PhabricatorCursorPagedPolicyAwareQuery {
 
   private $ids;
   private $phids;