Modernize policies in Paste and Macro

Summary:
Ref T603. Fixes T2823. This updates Paste and Macro.

  - **Paste**
    - Added default view policy.
    - I didn't add a "create" policy, since I can't come up with any realistic scenario where you'd give users access to pastes but not let them create them.
  - **Macro**
    - Added a "manage" policy, which covers creating and editing macros. This lets an install only allow "People With An Approved Sense of Humor" or whatever to create macros.
    - Removed the "edit" policy, since giving individual users access to specific macros doesn't make much sense to me.
    - Changed the view policy to the "most public" policy the install allows.
    - Added view policy information to the header.

Also fix a couple of minor things in Maniphest.

Test Plan:
  - Set Paste policy, created pastes via web and Conduit, saw they got the right default policies.
  - Set Macro policy, tried to create/edit macros with valid and unauthorized users.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2823, T603

Differential Revision: https://secure.phabricator.com/D7317