Allow Phabricator to write an access log using PhutilDeferredLog

Summary: Provide a configurable access log.

Test Plan:
Got a sensible-looking log including logged-in, logged-out, conduit, 404, etc:

  [Mon, 23 Apr 2012 20:08:12 -0700]	32599	orbital	-	epriestley	DifferentialCommentPreviewController	-	/differential/comment/preview/42/	http://local.aphront.com:8080/D42	200	65406
  [Mon, 23 Apr 2012 20:08:12 -0700]	32881	orbital	-	epriestley	DifferentialChangesetViewController	-	/differential/changeset/	http://local.aphront.com:8080/D42	200	72669
  [Mon, 23 Apr 2012 20:08:39 -0700]	32882	orbital	127.0.0.1	epriestley	DifferentialRevisionListController	-	/differential/	http://local.aphront.com:8080/D42	200	106444
  [Mon, 23 Apr 2012 20:08:54 -0700]	32867	orbital	127.0.0.1	epriestley	DifferentialRevisionListController	-	/differential/	http://local.aphront.com:8080/differential/	200	112229
  [Mon, 23 Apr 2012 20:09:05 -0700]	32530	orbital	127.0.0.1	epriestley	PhabricatorDirectoryMainController	-	/	http://local.aphront.com:8080/differential/	200	141350
  [Mon, 23 Apr 2012 20:09:10 -0700]	32598	orbital	127.0.0.1	epriestley	PhabricatorDirectoryCategoryViewController	-	/directory/6/	http://local.aphront.com:8080/	200	43474
  [Mon, 23 Apr 2012 20:09:12 -0700]	32880	orbital	127.0.0.1	epriestley	PhabricatorConduitConsoleController	-	/conduit/	http://local.aphront.com:8080/directory/6/	200	139340
  [Mon, 23 Apr 2012 20:09:15 -0700]	32868	orbital	127.0.0.1	epriestley	PhabricatorConduitAPIController	arcanist.projectinfo	/api/arcanist.projectinfo	http://local.aphront.com:8080/conduit/	200	128774
  [Mon, 23 Apr 2012 20:10:04 -0700]	32599	orbital	127.0.0.1	epriestley	Phabricator404Controller	-	/asdbmabdmbsm	-	404	38782
  [Mon, 23 Apr 2012 20:10:04 -0700]	32881	orbital	127.0.0.1	-	CelerityResourceController	-	/res/c9a43002/rsrc/css/aphront/request-failure-view.css	http://local.aphront.com:8080/asdbmabdmbsm	200	25160
  [Mon, 23 Apr 2012 20:10:57 -0700]	32882	orbital	127.0.0.1	epriestley	PhabricatorLogoutController	-	/logout/	http://local.aphront.com:8080/asdbmabdmbsm	200	40810
  [Mon, 23 Apr 2012 20:10:57 -0700]	32867	orbital	127.0.0.1	-	PhabricatorLoginController	-	/login/	http://local.aphront.com:8080/asdbmabdmbsm	200	42526
  [Mon, 23 Apr 2012 20:10:59 -0700]	32919	orbital	127.0.0.1	-	PhabricatorLoginController	-	/login/	http://local.aphront.com:8080/asdbmabdmbsm	200	49052
  [Mon, 23 Apr 2012 20:10:59 -0700]	32880	orbital	127.0.0.1	-	CelerityResourceController	-	/res/c80156c4/rsrc/js/application/core/behavior-dark-console.js	http://local.aphront.com:8080/login/	200	33166
  [Mon, 23 Apr 2012 20:10:59 -0700]	32868	orbital	127.0.0.1	-	CelerityResourceController	-	/res/4965d970/rsrc/css/aphront/dark-console.css	http://local.aphront.com:8080/login/	200	38078
  [Mon, 23 Apr 2012 20:10:59 -0700]	32599	orbital	127.0.0.1	-	CelerityResourceController	-	/res/pkg/8a5de8a3/javelin.pkg.js	http://local.aphront.com:8080/login/	200	40534
  [Mon, 23 Apr 2012 20:10:59 -0700]	32882	orbital	127.0.0.1	-	CelerityResourceController	-	/res/pkg/9c4e265b/core.pkg.css	http://local.aphront.com:8080/login/	200	41262
  [Mon, 23 Apr 2012 20:10:59 -0700]	32881	orbital	127.0.0.1	-	CelerityResourceController	-	/res/pkg/0c96375e/core.pkg.js	http://local.aphront.com:8080/login/	200	43720
  [Mon, 23 Apr 2012 20:10:59 -0700]	32921	orbital	127.0.0.1	-	CelerityResourceController	-	/res/caa86a45/rsrc/js/javelin/core/init.js	http://local.aphront.com:8080/login/	200	47566
  [Mon, 23 Apr 2012 20:10:59 -0700]	32867	orbital	127.0.0.1	-	CelerityResourceController	-	/res/f46289e9/rsrc/js/application/core/behavior-error-log.js	http://local.aphront.com:8080/login/	200	29328
  [Mon, 23 Apr 2012 20:10:59 -0700]	32919	orbital	127.0.0.1	-	CelerityResourceController	-	/res/7e62ff40/rsrc/image/phabricator_logo.png	http://local.aphront.com:8080/login/	200	25583
  [Mon, 23 Apr 2012 20:10:59 -0700]	32880	orbital	127.0.0.1	-	CelerityResourceController	-	/res/8c6200d3/rsrc/image/sprite.png	http://local.aphront.com:8080/login/	200	29829
  [Mon, 23 Apr 2012 20:11:01 -0700]	32868	orbital	127.0.0.1	-	PhabricatorOAuthLoginController	-	/oauth/facebook/login/  http://local.aphront.com:8080/login/	200	855931
  [Mon, 23 Apr 2012 20:11:02 -0700]	32882	orbital	127.0.0.1	epriestley789	PhabricatorLoginValidateController	-	/login/validate/	http://local.aphront.com:8080/login/	200	29793
  [Mon, 23 Apr 2012 20:11:02 -0700]	32881	orbital	127.0.0.1	epriestley789	PhabricatorDirectoryMainController	-	/	http://local.aphront.com:8080/login/	200	91638

Reviewers: jungejason, btrahan, vrana

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D2310