Basic image thumbnailing

Summary:
This is still very rough but provides basic support for generating image
thumbnails. I need to separate stuff out a bit but I'm going to integrate into
Maniphest before I hit the profile stuff so this seems like a reasonable
starting point.

Test Plan:
Generated some image thumbnails in various sizes.

Reviewed By: aran
Reviewers: jungejason, tuomaspelkonen, aran
CC: aran
Differential Revision: 333

resources/sql/patches/040.transform.sql

@@ -0,0 +1,10 @@
+CREATE TABLE phabricator_file.file_transformedfile (
+  id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  originalPHID varchar(64) BINARY NOT NULL,
+  transform varchar(255) BINARY NOT NULL,
+  unique key (originalPHID, transform),
+  transformedPHID varchar(64) BINARY NOT NULL,
+  key (transformedPHID),
+  dateCreated INT UNSIGNED NOT NULL,
+  dateModified INT UNSIGNED NOT NULL
+);