Added initial class for displaying invisible chars

Summary:
Fixes T11586. First pass at a class for displaying invisible characters. Still need to:
- Write a couple unit tests
- Add some styling to the .invisible-special spans
- Actually start using the class when displaying form errors to users

Currently this makes the string `"\nab\x00c\x01d\te\nf"` look like:

{F1812711}

Test Plan:
Unit tests all pass and run in <1ms:

{F1812998}

Reviewers: epriestley, #blessed_reviewers, chad

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley, yelirekim

Maniphest Tasks: T11586

Differential Revision: https://secure.phabricator.com/D16541

resources/celerity/map.php

@@ -146,6 +146,7 @@ return array(
     'rsrc/css/phui/phui-image-mask.css' => 'a8498f9c',
     'rsrc/css/phui/phui-info-panel.css' => '27ea50a1',
     'rsrc/css/phui/phui-info-view.css' => '28efab79',
+    'rsrc/css/phui/phui-invisible-character-view.css' => '6993d9f0',
     'rsrc/css/phui/phui-list.css' => '9da2aa00',
     'rsrc/css/phui/phui-object-box.css' => '6b487c57',
     'rsrc/css/phui/phui-object-item-list-view.css' => '87278fa0',
@@ -922,6 +923,7 @@ return array(
     'phui-info-panel-css' => '27ea50a1',
     'phui-info-view-css' => '28efab79',
     'phui-inline-comment-view-css' => '5953c28e',
+    'phui-invisible-character-view-css' => '6993d9f0',
     'phui-list-view-css' => '9da2aa00',
     'phui-object-box-css' => '6b487c57',
     'phui-object-item-list-view-css' => '87278fa0',