grid layout intuitiveness improvements

[matecsaj]

The order of children on the tree view does not change when using the grid layout and changing the row, and column numbers, the order of children on the tree view do not change. Maybe it is just me, but if the children were automatically sorted by row and column numbers, the tree view would be more consistent with how the application will render.

A related improvement might be to add a visual warning when a rendered node will be partially or fully obscured, perhaps a yellow dashed or solid outline in the tree and preview panes. A similar effect could be used for fatal errors, and red would be a natural color.