Add a column to immutably store the verified email of the version publisher

This is denormalized onto version deliberately. If people delete their
account, remove their email, etc we still have a way to attempt to
contact the publisher of a particular version in the event of a DMCA
complaint.

Author: carols10cents

migrations/2019-02-04-164501_add_published_by_email/down.sql

@@ -0,0 +1 @@
+ALTER TABLE versions DROP COLUMN published_by_email VARCHAR;

migrations/2019-02-04-164501_add_published_by_email/up.sql

@@ -0,0 +1 @@
+ALTER TABLE versions ADD COLUMN published_by_email VARCHAR;

src/schema.rs

@@ -909,6 +909,12 @@ table! {
         ///
         /// (Automatically generated by Diesel.)
         published_by -> Nullable<Int4>,
+        /// The `published_by_email` column of the `versions` table.
+        ///
+        /// Its SQL type is `Nullable<Varchar>`.
+        ///
+        /// (Automatically generated by Diesel.)
+        published_by_email -> Nullable<Varchar>,
     }
 }