Add content dashboards to the homepage

I switched the styling on the 1/3 + 2/3 columns to use the correct grid
styles, so that the widths were uniform down the whole homepage.

I had to do a bit a nasty in homepage.js in order to filter out the
GOV.UK content dashboard, which meant hardcoding a plus one into the
template. Not a massive fan but the other option I thought of would have
been to filter the list in the template which I liked even less.

I removed the hardcoded size from the transactions explorer tree-map
image as it seemed a little weird and I couldn't find a reason for its
existence.

The add3 style did not include the extra margins width it removed and
would never will 100% of the width. I have rectified this and pulled out
the widths to vars to be shared between col3 and add3.

The 'a strong' styling was added to make the two links on the homepage
match the style of the designs.

Conflicts:
	styles/common/columns.scss
Added device-type module for visit-visa
Updated label for users-at-each-step as per feedback on:

https://www.pivotaltracker.com/n/projects/911874/stories/65977104
Updated dashboard title, description and service url.
Merge pull request #527 from alphagov/feature/visa-access

device-type access
Merge pull request #525 from alphagov/content-dashboards-on-homepage

Add content dashboards to the homepage
Change Express route from use() to get()

Using the verb is more intuitive.
Fix basic authentication

With help from @lennym: https://github.com/alphagov/spotlight/pull/529#issuecomment-43990093

The use of middleware seemed intermittent at best, which isn't exactly
what you want for authentication.
Update GOV.UK frontend toolkit from 0.46.1 to 1.2

This is a big jump in version numbers but not such a big jump in
code changes.

https://github.com/alphagov/govuk_frontend_toolkit/compare/17aa587bbb578c4a551e56d39467c8fbda7482c7...9248f820e8a416070928d16fd71260198c6c681d

- Error colours now exist
- Improved CSS mixins
- Standard GOV.UK icons are now available
- Three quarters variable
Use new scale() mixin from frontend toolkit

Because shared code FTW.
Merge pull request #529 from alphagov/express-route-use-to-get

Change Express route from use() to get()
Merge pull request #531 from alphagov/update-govuk-frontend-toolkit

Update GOV.UK frontend toolkit
As James, I would like to tweet more precise links
Merge pull request #532 from alphagov/add-ids-to-link-to

As James, I would like to tweet more precise links
Remove need to generate json files for module stubs

Instead generate the module stubs at request time from the parent dashboard config
Swap fs sync methods for async versions

To avoid potentially blocking file IO.
SORN start page on GOV.UK has changed

Avoid an unnecessary redirect.
Merge pull request #534 from alphagov/update-sorn-start-page-url

SORN start page on GOV.UK has changed
Merge pull request #533 from alphagov/enhancement/remove-module-stubs

Enhancement/remove module stubs
Correctly bind function scope in view formatter test