By: Trevor Jeffery Truth is a factually interesting docudrama, with the unfortunate side effect of also being a huge downer – how can you chippily walk away from a film if its thesis is essentially “modern journalism is dead”? It’s 2004, just months before the American Presidential election, and Mary Mapes (Cate Blanchett) has got a story.  And as a producer for CBS’s documentary/news series 60 Minutes, she’s got a platform.  She’s uncovered that there…