GridContainer should have parameters for adding padding and spacing to children

[blackears]

It would be helpful to add parameters to GridContainer to automatically add padding and spacing to contained components. While you can technically do this by adding a lot of MarginContainers around the children of the GridContainer, it is really tedious to maintain them, especially in a large grid. I would suggest adding pad_left, pad_right, pad_top and pad_bottom parameters that would do the same thing as adding a MarginContainer to each child with its margin_left, etc, params set to those values. I'd also add a spacing_h and spacing_v parameters that would add spacing between cells of that many pixels in the horizontal and vertical directions (excluding the edges of the container itself). This would make adjusting the spacing of your grid easier and also make the component more similar to other table layouts, such as from CSS.