Add Sphinx and graphviz to the docker image

[borsna]

You can assign me to this one.

To run Sphinx we need #38 and for Graphviz a fix for #160

[DanSmith]

We are thinking that we will have a build and deploy scripts which will be run by CI on commits and pull requests to a cogs model's repository. Something similar to the scripts in:

https://gitlab.com/c2metadata/sdtl-cogs/tree/master/build

We can still add it to the publisher also, but how would that look? Should we call sphinx-build directly with a bunch of arguments? Or a path to a user provided sphinx make file with just a sphinx target such as dirhtml?

[borsna]

I think keeping the makefile is the most flexible way to go.
Right now the makefile is generated by a build in template in cogs so adding additional output target from sphinx would not work.

If cogs check the Settings directory for a custom make-file when generating the Sphinx output rst-files additional targets and settings would be posible, if no file exist just do a default makefile.

The publish command would then just call the the makefile in the sphinx output directory specified via a path and also take additional arguments.

Dont know if this makes sense :)