inspect multiple boxes and display them in a single figure

[quaquel]

closes #124

Adds an optional keyword argument ax to PrimBox.inspect to be used in conjunction with style='graph'. Ax can be a single Axes or a list of Axes instances of the same length as i. If used, each box in i is plotted in separate Axes.

Rather that try to solve the axes layout as suggested in #124, it is left to the user to setup the figure to their liking. See sd_prim_flu.py for an example usage.

[coveralls]

coverage: 80.251% (+0.05%) from 80.206%
when pulling 55b5a44 on inspect_graph
into 2002532 on master.

[EwoutH]

Thanks for implementing this, I will try to review it this week.

[quaquel]

Just a simple reminder that it would be great if you could take a quick look at this so I can merge it.

[EwoutH]

Thanks, I put it on my list for Monday.

To give some context, I'm now really in a hard push to get my thesis started. As always, the things I find most interesting are also the hardest and biggest. Then this requires to get a full overview of the system to properly identify the gaps - and then selecting a feasonable one. So that consumes most of my energy right now.

Also, maybe it would be good to talk about my formal role in the workbench maintenance again. When I was TAing in EPA1361 and after that working on the MPIEvaluator is was a relatively low effort to do it on the side (and a great learning experience - it still is), I now notice takes a bit more effort to switch to it.

[EwoutH]

Looks great! I really like the warnings for catching invalid input.

Only thing I would like to see is another test with multiple boxes and axes, further everything looks good to me!