Revisit migration tasks

* Move migration scripted tasks to the stream folder naming them .task.php.
* Add a MigrationTask abstract class to server as the base of migration
  tasks.
* Move the migration tasks from class.upgrader to the new task files
Merge remote branch 'jared/feature/crypto' into feature/crypto-upgrade
Change email en/decryption to use crypto class
Drop old mcrypt class
Use 16-bytes iv.
Upgrade patch for 16fcef4a13d6475a5f8bfef462b548e2
Fix regression on upgrader