Add ability to set top level Grid properties from within ECL

[pml-lnr]

Currently the default layout seems to try and render all requested visualizations within the initial space shown in the Dermatology window, which is problematic if requesting a larger number of graphs as they are each so small as to be unusable. It would be very helpful if there was a simple way to specify max columns or minimum pixel dimensions, something to ensure the initial view was useful. Is it possible to expose some top-level Grid properties so they can be set via Visualizer as well?

I'm happy to provide additional details or examples if that would be helpful. Thanks!