More constant fixes

Transition::ORIENTATION_XXX -> Transition::Orientation::XXX
Image::FORMAT_XXX -> Image::Format::XXX
Image::_function() -> Image::function() // private methods should not start with '_'
DrawPrimitives::drawColor() -> DrawPrimitives::setDrawColor()

And fixes Premultiplied Alpha in PVR v3 images
And tests are updated with the new functions