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