By Emily Williams We’ve written before ​about the financial troubles plaguing the Prisa Group, owner of Santillana, one of Spain’s largest publishers.  ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​The Economist, in its colorful way, now reports that the group has traded a big chunk of its family ownership in return for a lifeline investment from Liberty Acquisitions, an investment group whose sponsors include Nicolas Berggruen, “an art …