By default folder for stream frames.
base naming syntax is 
	last_digit_of_stream_id / stream_id / frame_time_in_seconds.jpg
resized images: 
	last_digit_of_stream_id / stream_id / frame_time_in_seconds_160x120.jpg 
	
images_not_available is the base missing image that is sent when no image can be found in range

Eventually stream images will be moved over to mediaWiki image directory
once streams are better tied into uploaded files. 