Improve `matrix` object

Since it basically has the same properties that the `block-list` objects we can make proper use of the DRY principle and @extend it.
Switched base font-family to use a variable

The base font-family is a design choice. By using a variable we can set
it once and avoid having to override it
Add float none helper
Add text helper comment
Add margin and padding helpers
Improve go class
Improve hidden content helper
Merge remote-tracking branch 'kevva/fix/matrix' into fix/matrix

Fixes #112
Add !important flags to helpers
Wrap hidden elements CSS up in a mixin
[refs #94] Reinstate links’ initial underline
[refs #94] Remove links module altogether
Switched base font-family to use a variable

The base font-family is a design choice. By using a variable we can set
it once and avoid having to override it
Merge remote-tracking branch 'waynemoir/master' into tkt-150
[refs #150] Set base font family via variable

Fixes #150
Tidy up file formatting
Use csswizardry-grids style grid system

Also add mobile-first approach; fixes #137
Add push and pull for lap-and-up

Also tidy up how push and pull are included. Fixes #148
Merge branch 'feature/grids' into v5.0
Merge branch 'feature/helpers' into v5.0