IMGAPI-241: update IMGAPI signature auth usage to the latest http-sig spec
IMGAPI-241: update IMGAPI signature auth usage to the latest http-sig spec

Also update to latest deps, notably from restify ~2.4.1 to 2.6 which
will fix static serving of /docs/ not working.

numericillustration/sdc-imgapi,numericillustration/sdc-imgapi,joyent/sdc-imgapi,joyent/sdc-imgapi,joyent/sdc-imgapi,numericillustration/sdc-imgapi