Enhancements to grid after recent client projects

* Reduce specificity by not nesting grid columns within the grid
wrapper. This helps when overriding widths in media queries
* Reduce number of internal extends as this can lead to styles not
getting applied as Sass chokes on processing the output. Weird.
Merge branch 'fix/specificity'

* fix/specificity:
  Enhancements to grid after recent client projects