Add quality factor to octet-stream mediatype

[cgorman]

Depending on the IMS implementation, they may return octet-stream when image/jpeg is available because octet-stream appears higher on the list of acceptable media types. This PR adds q=0.9 to the field value.

Fixes #80

[cgorman]

I've tested this with Slim for a month or so using patch-package for local and remote IMS instances (dcm4chee, google, and GE) and it has been working well FWIW