Fix contrast and border on iOS

It appears safari on ios8 respects border/background-color settings, which means that the white+no border were rendering these inputs practically invisible on ios8

This commit adds a class to both of the input[type=text] so that we can appropriately scope the white background/grey border to text inputs only. I've used a class instead of input[type=text] so that it works in ie6 too.

With this added we no longer need to overwrite the width and the border which means ios does the default contrasty thing that we want.
Remove li scope

don't need to scope these styles to an li so remove it.
Remove font handling here

We don't need to handle font sizes for responsive because the @include deals with it.
Merge pull request #114 from alphagov/fix-checkbox-contrast

Fix checkbox contrast