Extend grid placeholders with grid-columns-all

I tried to only use placeholders, no classes. Example (SCSS syntax):

    .myClass {
        @extend %grid-75;

        @media screen and (max-width: $media-query-breakpoint) {
          @extend %grid-100;
        }
    }

But like this the gutters were missing. This seemed to be because the grid classes extend the grid-columns-all placeholder, but the grid placeholders themselves don't.

So I made the placeholders extend grid-columns-all in the vars partial, and removed the columns definitions in the grid-base partial, which shouldn't be necessary anymore then.

I hope I didn't make a mistake here, which prevented the gutters from working in the first place, or overlook any side-effects my change might have.