Set header, footer and generic banner alignment

- Set footer wrapper and footer meta to use outer and inner blocks from
front end toolkit and remove duplicate padding

- Remove left and right padding from header, increase width for IE8 and
below and remove use of old media down mixin
- Use $gutter variables from front end toolkit

- Add layout file, which creates classes for outer and inner block,
using the _grid_layout file in the front end toolkit
- Add outer and inner blocks for cookie message alignment

This ties in to this [comment on a pull request in the front end toolkit](https://github.com/alphagov/govuk_frontend_toolkit/pull/91#issuecomment-39565969)