Feature request: Create layout with multiple plots at once without iterated splitting of plots

[llvs]

The issue is related to the UI changes from PlotJuggler 2.x to 3.x: In Plotjuggler 2.x pressing the add row/column button would add plots to all existing rows/columns. That way, there was less flexibility in available layouts but it was rather easy to create a larger array of plots (say, e.g., 6 rows with 3 plots per row). Now in 3.x the only way seems to press the split button for each plot. This leads to a lot of clicking if I want to observe, e.g., all the states and covariances for a large filter.

Proposed enhancement:
Offer to create an evenly split array layout of plots as a starting point, i.e., let me enter "6x3" somewhere to obtain a layout containing 18 equally sized plots in a 6 rows 3 columns layout inside the current plots tab.