Generalize the markup engine factory

Summary:
This thing services every app but it lives inside Differential right now. Pull
it out, and separate the factory interfaces per-application.

This will let us accommodate changes we need to make for Phriction to support
wiki linking.

Test Plan: Tested remarkup in differential, diffusion, maniphest, people,
slowvote.
Reviewed By: hsb
Reviewers: hsb, codeblock, jungejason, tuomaspelkonen, aran
CC: aran, hsb
Differential Revision: 646

src/applications/project/controller/profile/PhabricatorProjectProfileController.php

@@ -111,8 +111,7 @@ class PhabricatorProjectProfileController
        $profile->getBlurb(),
        '//Nothing is known about this elusive project.//');
 
-    $factory = new DifferentialMarkupEngineFactory();
-    $engine = $factory->newDifferentialCommentMarkupEngine();
+    $engine = PhabricatorMarkupEngine::newProfileMarkupEngine();
     $blurb = $engine->markupText($blurb);
 
     $affiliations = $project->loadAffiliations();

src/applications/project/controller/profile/__init__.php

@@ -7,10 +7,10 @@
 
 
 phutil_require_module('phabricator', 'aphront/response/404');
-phutil_require_module('phabricator', 'applications/differential/parser/markup');
 phutil_require_module('phabricator', 'applications/files/uri');
 phutil_require_module('phabricator', 'applications/maniphest/query');
 phutil_require_module('phabricator', 'applications/maniphest/view/tasksummary');
+phutil_require_module('phabricator', 'applications/markup/engine');
 phutil_require_module('phabricator', 'applications/phid/handle/data');
 phutil_require_module('phabricator', 'applications/project/constants/status');
 phutil_require_module('phabricator', 'applications/project/controller/base');