Better import handling: try to import all cards, and show to the user those which cannot be imported

[Altonss]

I thought about a possible enhancement related to the issue #661 . Instead of just quitting the whole import, we could import the cards that are "compatible"/"readable" by the import script and just don't import the once that fails. After the import a popup could show up saying: "1 card could not be imported because of a formatting error". But this is just an enhancement idea and not a priority at all :)