Conpherence V1

Summary: it's ugly. but it works. basically. See T2399 for a roughly prioritized list of what still needs to happen.

Test Plan:
- created a conpherence with myself from my profile
- created a conpherence with myself from "new conpherence"
- created a conphernece with another from "new conpherence"
- created a conpherence with several others
- created a conpherence with files in the initial post
 - verified files via comment text ("{F232} is awesome!") and via traditional attach
- edited a conpherence image
 - verified it showed up in the header and in the conpherence menu on the left
- edited a conpherence title
 - verified it showed up in the header and in the conpherence menu on the right
- verified each widget showed up when clicked and displayed the proper data
 - calendar being an exception since it sucks so hard right now.

Reviewers: epriestley, chad

Reviewed By: epriestley

CC: aran, epriestley, chad, codeblock, Korvin

Maniphest Tasks: T2301

Differential Revision: https://secure.phabricator.com/D4620

src/infrastructure/markup/PhabricatorMarkupEngine.php

@@ -480,6 +480,22 @@ final class PhabricatorMarkupEngine {
     return $mentions;
   }
 
+  public static function extractFilePHIDsFromEmbeddedFiles(
+    array $content_blocks) {
+    $files = array();
+
+    $engine = self::newDifferentialMarkupEngine();
+
+    foreach ($content_blocks as $content_block) {
+      $engine->markupText($content_block);
+      $ids = $engine->getTextMetadata(
+        PhabricatorRemarkupRuleEmbedFile::KEY_EMBED_FILE_PHIDS,
+        array());
+      $files += $ids;
+    }
+
+    return $files;
+  }
 
   /**
    * Produce a corpus summary, in a way that shortens the underlying text