Qt4 backend improvements

Hi,

> There
> may be a reason it was done in the less straightforward way that aren't
> obvious to you or I (perhaps to ease embedding... just guessing).

I don't think we can use the QMainWindow's addToolBar for this. It creates

a

single toolbar for the entire window, but what if we want to add two
canveses, each with its own toolbar, in a single window? I am writing an
application that does this.

Well, technically this is not a problem, since you can add several toolbars
with addToolBar. But well, you are right, this would look awkward, two
times the same toolbar... But anyhow, I am calling addToolBar in the class
FigureManagerQT, which is not able to handle more than one plot in a
window it seems to me (am I missing something?). If, on the other
hand, you create your own QMainWindow, there is no problem putting the
toolbar like it was done classically. I added an example for that to the
patch request ID 1828848 (Qt4 backend improvement). I don't know your
code, but it is possible, maybe even probable, that it works even
with my modifications, as I did not change the class structure.
Only possible incompatibilities I could see is if you are inheriting
FigureManagerQT and doing something in there.

So in the end I think my patch is still a good idea. It might be needed
to change it to keep compatibility with old code, though.

Greetings,

Martin