Further mitigate BREACH by reducing reflectiveness

Summary:
Ref T3684. The URI itself is reflected in a few places. It is generally not dangerous because we only let you add random stuff to the end of it for one or two controllers (e.g., the file download controller lets you add "/whatever.jpg"), but:

  - Remove it entirely in the main request, since it serves no purpose.
  - Remove query parameters in Ajax requests. These are available in DarkConsole proper.

Also mask a few things in the "Request" tab; I've never used these fields when debugging or during support, and they leak quasi-sensitive information that could get screenshotted or over-the-shoulder'd.

I didn't mitgate `__metablock__` because I think the threat is so close to 0 that it's not worthwhile.

Test Plan: Used Darkconsole, examined Requests tab.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3684

Differential Revision: https://secure.phabricator.com/D6699