Added initial table structure
Renamed order DCA
No need for our ptable hack anymore, we don't have a PID field
Add all ctable items so they can be deleted by reviseTable
Fix and clean database.sql
Renamed tl_iso_collection.status to tl_iso_collection.orderstatus
Renaed tl_iso_collection_item to tl_iso_collection_product
Store class name for collection and collection products

This can later allow to use an external table (not tl_iso_products) for collections.
The abstract class should not implement the interface
strTable and ctable is the same for all collections (by default)
Updated cart session management
Only show collections of type=Order in the backend
Fixed call to class variable
Make sure collection model returns only results of its type
Renamed cart_id to source_collection_id in collection table
Store database ID from product collection table in collection_id (not cart_id) property
No need to fetch the model again

The new model implementation in Contao 3 automatically sets the ID
when saving a new records.
Improved model queries
Deleted old collection tables, renamed downloads table
Mayor improvements on Automator::deleteOldCars() method