Default horizontal split of plot window

This issue was created automatically from an original Mantis Issue. Further discussion may take place here.

Since version 3.14.0, the plot window is split horizontally by default when a new plot is generated, e.g. by the PlotSelectionOverTime filter. In ParaView 3.12, it was split vertically, which I prefer. It would be good to enable the user to influence this behaviour, e.g. via the settings.

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