Hard-code 6 scale factors
Hard-code 6 scale factors

Our default / assumption is 6 progression levels, so the IIIF server
should only report 6 scale factors as being ideal.

uoregon-libraries/rais-image-server,uoregon-libraries/rais-image-server,uoregon-libraries/rais-image-server,uoregon-libraries/rais-image-server