Stephen Spielberg is one of only a few artists and the only film director to be awarded the Philadelphia’s Liberty Medal for humanitarian work.   Bill Clinton presented it to him Thursday at the National Constitution Center.  An audience of local and national dignitaries watched clips of Spielberg’s ‘The Color Purple’ ‘Amastad’ ‘Saving Private Ryan’ and his finest achievement in cinema ‘Schindler’s List.’  But the clips of WWII soldiers and Holocaust survivors for Spielberg’s international ‘Shoah Project’ was the most moving part of the evening.