Fix flags
Remove stupid column_count and using DownloadTableModel internal enums
Fix getting super class data

It doesn't work anymore in qt5, I don't know why or how!
Validating value at data()
Get download column value

Since SQL model removal, this shold be implemented by bare hands
Validating role
Set downloadholder data

yep, again since SQL model removal this also should be implemented
emit datachanged signal to let the world know about data changes
Implement insertRows
Using DownloadHolder class instead of dynamic yoDownet based Download class