Modify default column widths for all layouts

[salcode]

See #108 for changes in default layout

[salcode]

See branch change-col-other-layouts-119 for proposed changes.

[salcode]

Ok, I've been reviewing my previous preposed changes, which looked like this for sidebar-content-sidebar

I think this is simply too narrow for the content column column. Instead I think we should wrap the secondary sidebar down to the next line on the sm screensize.

[salcode]

As a rule, I think:

• at the md size, 3 should be the minimum number of columns
• at the sm size, 4 should be the minimum number of columns