initial set of Dockerfiles for 3 basic images

images are:

• base: jnlp-slave + upgrade + build tools
• tox: base + pg10 + up to date pip, coverage, pylint, codespell and radon
• sphinx: tox + up to date sphinx + dependencies required to be able to build SWH's doc

Also comes with a makefile to build those images and check ther are up to date.