Persistent template rows

In order to make the template rows compatible with the persistence mechanism I had to change quite some things.
* I changed the persisted data from the ```.to_hash``` data to ```.render```. This makes it easier to read the values and allows to change the order of the rows without breaking the persistence.
* ```.to_hash``` new returns only one row for template rows (no subrows anymore)
* The persisted data is not archived anymore. This fixes crashing the App without any notice after unarchiving several times.

The code got a bit complex and I would like to take some time for refactoring afterwards.