* started working on native image support
 * restructured opencl image format querrying + created a "opencl image format" -> "oclraster image format" mapping (note: not all oclraster image formats are supported by opencl, e.g. UINT_64 or FLOAT_64)
 * if (native) image based backing is requested when creating an image, but the format is not supported, buffer based backing will be used
 * note: framebuffers will of course only accept images with buffer based backing