Allow qt plugins to specify a preference for relative positioning

[scpeters]

When plotting multiple topics in rxplot, each topic would be displayed in its own vertically-stacked subplot. Here's an example from a drcsim tutorial.

Based on the discussion of rqt_common_plugins issue 86, I was able to plot topics in separate subplots using rqt_plot, but they are tiled horizontally rather than vertically.

It's nice to have plots stacked vertically, so their timelines are aligned. More generally, it would be nice if rqt plugins could specify a preferred relative position.

[ablasdel]

@DorianScholz Any ideas on how much work this might be?

[dirk-thomas]

I will add an option to make this possible via the command line. I am not yet sure if it should/could also be exposed in the plugin api.

[dirk-thomas]

I prepared a patch on the branch orientation but the result is not yet great. It does work reliable for multiple dock widgets since restoreState seems to overwrite the orientation.

I filled a ticket at https://bugreports.qt-project.org/browse/QTBUG-32749 - lets see what the response on this will be.

[dirk-thomas]

In the meantime the ticket has been moved but the problem is still the same with newer Qt versions: https://bugreports.qt.io/browse/QTBUG-32749