Big update

[kjake]

• Switch image to newer debian base, slim version
• Remove installation of unneeded packages
• Switch from building netatalk from source to using pre-built .deb packages
• Update docker-entrypoint.sh to specify path to the afp.conf as it is different from the new packaged default

I've forked this myself on Docker Hub (https://hub.docker.com/r/kjake/netatalk/) as it was a big departure from your original intent of building from source; however, I wanted to give you the opportunity to pull my changes back into your version. I have also setup my Docker Hub Repo to autobuild whenever debian pushes a new version, so my repo will stay security patched.

[kjake]

even though I thought I tested this well, I realized now that I accidentally removed tracker from the install... whoops!