Change created_at and updated_at to use standard INT column type

[cuteapoot]

Currently, the created_at column is INT, but updated_at was VARCHAR. I updated it so both would be INT with 'size' => 'normal', 'unsigned' => FALSE. We may need to alter the worker that inserts data into the db, because it looks like created_at is just including the year and updated_at has the full ISO timestamp, despite supposedly using strtotime before saving those column.