Fixed seralization error in responsetransporter, when changes containing date's.
Fixed templatedossier tests.

With the fix https://github.com/4teamwork/ftw.testbrowser/pull/17,
the ftw.testbrowser handles the checkbox now correctly, so some changes in the
templatedossier tests was necessary.
Merge pull request #466 from 4teamwork/pg_task_reponse_transporter_date_fix

Fixed seralization error in responsetransporter, when changes containing dates.