Make Thread-Topic human readable

Summary:
Some e-mail clients display this header and it needs to be constant.

This is somehow involved but I doubt that there is a simpler solution.

Test Plan:
Applied SQL patch.
Commented on revision, commented on commit, changed package.
Verified that the `Thread-Topic` has constant and human readable value.

Reviewers: epriestley

Reviewed By: epriestley

CC: ola, aran, Korvin

Differential Revision: https://secure.phabricator.com/D2745

resources/sql/patches/threadtopic.sql

@@ -0,0 +1,14 @@
+ALTER TABLE {$NAMESPACE}_differential.differential_revision
+  ADD originalTitle varchar(255) NOT NULL AFTER title;
+UPDATE {$NAMESPACE}_differential.differential_revision SET
+  originalTitle = title;
+
+ALTER TABLE {$NAMESPACE}_owners.owners_package
+  ADD originalName varchar(255) NOT NULL AFTER name;
+UPDATE {$NAMESPACE}_owners.owners_package SET
+  originalName = name;
+
+ALTER TABLE {$NAMESPACE}_maniphest.maniphest_task
+  ADD originalTitle text NOT NULL AFTER title;
+UPDATE {$NAMESPACE}_maniphest.maniphest_task SET
+  originalTitle = title;