Avoid usage of "latest" or git-master dependencies

[squix78]

In the docker file we use "FROM resin/rpi-raspbian" which uses the latest release of the rpi-raspbian image. This can introduce instability when the parent image has changed in the meantime. Similarly cloning the master version of a git-repo in the Dockerfile can lead to inconsistent behavior if no tag has been used. If the image is built at different points in time the resulting image can look different with every build.

This can be compared to a maven release which should not have dependencies to any unreleased version of other libraries.

In addition the image on dockerhub should get tagged not just with "latest" but with versions

Thanks to @marschall for the input.

Here some more reading about the topic:
https://medium.com/@mccode/the-misunderstood-docker-tag-latest-af3babfd6375
http://blog.benhall.me.uk/2015/01/dockerfile-latest-tag-anti-pattern/
http://container-solutions.com/docker-latest-confusion/