removed 'viewPortWidth/Height' properties of Starling class; instead, added 'backBufferPixelsPerPoint' (refs #618)

I didn't like the previous solution — somehow, it was not intuitive. Now, it's a straight-forward multiplication to get to the actual pixel values, and the existing properties (backBufferWidth/Height) work just as in Starling 1.5.
changed import order in IDEA modules

(No idea why, but otherwise it did not reference Starling correctly any longer :| )
updated version to 1.6
updated change log for verion 1.6rc
updated starling.swc for v1.6rc