Build and execute notebooks with nbsphinx

[jenshnielsen]

This tries to simplify the execution of notebooks as part of the build process. This seems to solve
the issue building notebooks on windows and simplifies the logic. Currently all notebooks are
executed unless metadata is added to mark them not executable. The execution can be customized on a per notebook basis to allow longer timeout or cells raising errors. We make use of this in a few examples

Execution of notebooks can be skipped completely by setting an env variable for speed

In the process I fixed some broken code in a few notebooks and some broken links.

It is now possible to build the docs in two ways from both windows (with cmd/bat) files and from
osx/linux with Makefiles.

The target htmlapi will execute all notebooks that can be executed.
The target htmlfast skips the notebook execution and is better suited for rapid iterations

TODO:

• Document how this is done. Especially that you need to disable execution of driver notebooks and the way to skip the notebook execution. We should perhaps even have a make target that does this.
• There still seems to be one failure that I have not tracked down yet

[jenshnielsen]

@QCoDeS/core I think this is ready for review

[jenshnielsen]

This is likely to conflict with #1309 so we should decide which one goes in first

[Dominik-Vogel]

I will take a look at this PR and will hopefully learn enough to be able to merge it into #1309. So this one can go first.

[astafan8]

all cool! really, thanks for cleaning this up!

one thing: is there going to be a small description for developers about how this works? i'm interested in the following: what to do if i am adding a new notebook, when should i enable/disable its execution and how (well, i know how, but it's nice if that's documented), how do i enable/prevent sphinx from building the notebook. (please ignore this request if all of this is neatly covered in sphinx docs, and there is nothing specific/special to our setup within qcodes)

[jenshnielsen]

@astafan8 Yes we should probably have a documenting QCoDeS page that includes some of this along with best practice for documentation. Google style and so on. I added part of it to the writing drivers notebook because I figured that was the most likely place for new users to look

[astafan8]

@jenshnielsen ok, let's say that for now the info that you wrote in the driver docs is enough.