Update govuk frontend toolkit npm to 1.7.0
Update layout.scss

Use new grid layout mixins from the front end toolkit to define:
- A single page container
- A grid row for grid columns to sit in
- Grid column widths
Update index to use new grid layout mixins

- Remove additional page wrappers
- Remove inner block
- Use new .grid-row and .column- classes
Update snippets to use new grid layout mixins

- Remove inner block
- Use new .grid-row and .column- classes
Update node sass for placeholder support
Update mocha
Remove margins set by Service Design Manual header
Duplicate front end toolkit placeholders as mixins

Placeholder Sass compilation issue, duplicating site-width-container
and grid-row as mixins within _helpers.scss until it can be resolved
Set header bar to use site-width-container mixin

- Remove styles for .inner-block and add a comment to update this in
the GOV.UK template
Add padding to example boxes

- Set padding on example boxes now .inner-block has been removed
Remove reference to deleted content id

- Content is no longer required
- Bump up font size on main
Make list styles more specific

Only apply top and bottom margins to bulleted and numbered lists.

This was affecting the breadcrumb (adding a bottom margin under the
list items, moving the bottom border on the list) which isn’t what we
want to happen.
Update grunt-sass npm
Update chalk npm
Remove wrapper and inner divs

- Change main id #wrapper to #page-container
- Remove #content and .inner-block divs
- Rename .grid-wrapper to .grid-row
- Rename .grid- to .column-(fraction)
Add helper mixins

- Use mixins until libsass supports the placeholder syntax used by the
front end toolkit
Update grid example page

- Remove lorem
- Add javascript to toggle background colours on grid cells
Merge pull request #37 from alphagov/update-govuk-frontend-toolkit-grid-layout

Update govuk frontend toolkit grid layout