Create responsive padding / margin utilities

As per gitlab!61503 (comment 573049564) we need a selection of responsive utilities:

• pr-md-0 => gl-md-pr-0
• pl-md-2 => gl-md-pl-3
• mb-2 mb-md-0 => gl-mb-3 gl-md-mb-0

Let's add them and update the main project 😄