Extensions are mandatory and only if files are enabled
Fixed invalid SQL statement
Re-implemented downloads attribute

Code duplicated from ContentDownloads element
CS
We should not need to clean field values, the Attribute object can handle this
System columns are now defined in the DCA
Removed unused use statement
Fixed base price calculation with price object
Can now pass custom options to an attribute when generating
Can set custom sorting in the template for downloads attribute
Moved generator routines to separate methods
Overwrite type only if we can find it
Set attribute class directly so we don't need to register it
Use tax class of price tiers
Added PriceTiers attribute

Not registered but used to generate price tiers of a product
Fixed Downloads model
Moved public static getMetaData to global Isotope object
CS
Drop collection caches after using copyItemsFrom
Do not allow to delete a product if it has been sold