Warn of SetStatus() between Prepare() and Cleanup() more thoroughly

[jd41]

For me, the warning in the notes in that section was not enough. I changed some things in the simulation code I am working with, including replacing nest.Simulate() by nest.Prepare()/nest.Run()/nest.Cleanup(). After that, there was some SetStatus() between Prepare() and Cleanup(). I didn't catch the note that SetStatus() should not be called between Prepare() and Cleanup(). I continued making other changes, because the code seemed to continue to work. At some point, I realized that there were no/not enough spikes recorded anymore. Tracking down that the problem was in replacing Simulate() by Run() took me on the order of a week, and I only recognized the current warning in the documentation after reverting that change just to see what happens.

[Silmathoron]

@apeyser would it be possible to detect this and raise an error? Did you already introduce variables that would tell that cleanup has not been called yet?
I think calling SetStatus in that case should directly raise an error, we should not let users be able to do this unknowingly...

[jd41]

I wrote issue #1773, in which I propose/ask if it would work to do the prepare/run/cleanup stuff on the PyNEST level and hide that complexity from the PyNEST user.

[stinebuu]

We need to fix the underlying issue (throwing error when SetStatus is called), thus we are not merging this. See also #1773.