Add headers to allow use with project-fifo

I found out if I did the following and added the `Access-Control-Allow-...` headers in this PR, I can use @licenser 's project-fifo to load my custom datasets that are served from this smartos-image-server vm

From the VM running fifo:
sed -i 's/datasets.at/`my-image-server-ip`/' /opt/local/fifo-jingles/app/scripts/config.js