External file save reloaded

adds the possibility to pass through the intent's extra bundle by means of the key MediaStore.EXTRA_OUTPUT (not sure if that is the right choice though) a path to which the image should be saved to when pushing the save button. If that path if supplied, the saving to temporary files is overridden. For that I had to extract the retrieval of the file path into a separate method, to be able to check the case of output path availability.