Add the rest of the "Debug/Developer" config group.

Summary:
- Adds the rest of the group as per T2255.
- Adds a pht() around the `$developer_warning` in `PhabricatorStandardPageView`.

Test Plan:
- Viewed new config options.
- Triggered a fake warning to make sure I didn't break error callouts.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2255

Differential Revision: https://secure.phabricator.com/D4333