Add spacing and center for Grid

[mytdragon]

Hi,

I would like to give you my thanks first because your Grid component really helped me for my project.

I edited it on my local to fit my need but if the changes interest you, feel free to accept or decline it :)

I didn't include it in the PR but I'm currently working on a Grid component that support grouping (and collapsing), it works almost fine, just a re-render of the last row of group each time I scroll up. I would love if there was a component for it :)

Kind Regards, MYT