Make "public" pastes meaningfully visible to logged-out users
Summary:
- Introduce shouldAllowPublic(), indicating that logged-out users are OK in a controller if the install is configured to permit public policies.
- Make Paste views and lists allow public users.
- Make UI do sensible things with respect to disabling links, etc.
- Improve behavior of "you need to login" with respect to policy exceptions and Ajax requests.
Test Plan: Looked at "public" paste, saw all unavailable UI disabled, clicked it, got appropraite prompts.
Reviewers: vrana, btrahan
Reviewed By: vrana
CC: aran
Maniphest Tasks: T603
Differential Revision: https://secure.phabricator.com/D3502