photosurface example: simplify PinchArea usage; fileUrls; license

FileDialog.filePaths was changed to fileUrls.  No need to do so much
scripting because the PinchArea.target takes care of the math already,
and with better rotational symmetry too.  Example QML should have a
BSD license.

Change-Id: I892292574c81c032d948c1c2d4924fc7127dd008
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>