Image macros for Phabricator!

Summary:
Added long waited image macro support for differential and others.

Test Plan:
Tried a couple of different macros and made sure they appear nicely
in the comment preview. Made sure that the normal comments are shown
correctly.

Reviewed By: epriestley
Reviewers: epriestley
CC: jungejason, tuomaspelkonen, epriestley
Differential Revision: 129

resources/sql/patches/030.imagemacro.sql

@@ -0,0 +1,5 @@
+CREATE TABLE phabricator_file.`file_imagemacro` (
+       `id` int unsigned NOT NULL auto_increment PRIMARY KEY,
+       `filePHID` varchar(64) NOT NULL,
+       `name` varchar(255) NOT NULL
+);