DarkConsole: fix rendering, move request log, load over ajax

Summary:
This accomplishes three major goals:

  # Fixes phutil_render_tag -> phutil_tag callsites in DarkConsole.
  # Moves the Ajax request log to a new panel on the left. This panel (and the tabs panel) get scrollbars when they get large, instead of making the page constantly scroll down.
  # Loads the panel content over ajax, instead of dumping it into the page body / ajax response body. I've been planning to do this for about 3 years, which is why the plugins are architected the way they are. This should make debugging easier by making response bodies not be 50%+ darkconsole stuff.

Additionally, load the plugins dynamically (the old method predates library maps and PhutilSymbolLoader).

Test Plan:
{F30675}

  - Switched between requests and tabs, reloaded page, saw same tab.
  - Used "analyze queries", "profile page", triggered errors.
  - Verified page does not load anything by default if dark console is closed with Charles.
  - Generally banged on it a bit.

Reviewers: vrana, btrahan, chad

Reviewed By: vrana

CC: aran

Maniphest Tasks: T2432

Differential Revision: https://secure.phabricator.com/D4692