Added init script for OctoPrint and easier way for local build configuration

This PR changes OctoPi such that the ``octoPrintStart`` script is no longer needed but ``/home/pi/oprint/bin/octoprint`` is installed as a system service via init script and entries in ``rc*.d``.

Also switches build to use OctoPrint's ``setup.py`` which takes care of resolving requirements and the like.

Since I found it a bit risky having to edit ``src/config`` just for setting the image path I also introduced a mechanism to auto detect that based on a new folder in which to place images (the most recent zip file matching the file name pattern ``*-raspbian.zip`` is used) and added a mechanism to try to load local configuration overwrites from a file ``src/config.local`` if it exists (which is not supposed to be checked in and therefore added to ``.gitignore``, just like zips located at ``src/image``)

Sorry for the weird merges there, for whatever reason git was of the opinion that I wasn't fully up to date with the current devel branch after the first merge.