Fix TGMarker bitmap channel swap (#2168)
Fix TGMarker bitmap channel swap (#2168)

* Remove BGRA->RGBA pixel conversion in TGMarker

* Use DeviceRGB colorspace when converting images to bitmaps on iOS

* Add correction to alpha un-premultiply for rounding down
tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es