FR: "Import" should support dual card names (flip cards, split cards, adventures, etc.)

If I use deck editor's "import" button and enter a line like this:

> 1 Murderous Rider // Swift End

It's unable to find the card. It works OK if I delete the "// Swift End". It would be nice if it supported the full name.

Start at the deck editor's "Import" button and trace how each imported line is parsed and matched against card names. Verify the behavior with a line containing "Murderous Rider // Swift End" and confirm that importing the full dual-card name succeeds without requiring the second name to be removed.

Written by the indexing model from the issue text.