Remove smart answers scoped styles from static

Add them to smart answers in order to scope smart answers styles to
make smart answers easier and quicker to update.

https://www.agileplannerapp.com/boards/105200/cards/6024
Updating footer link for /browse/housing

The browse category has been renamed to /browse/housing-local-services.
Merge pull request #475 from alphagov/update_housing-link-in-footer

Updating link for /browse/housing in the footer
Merge pull request #472 from alphagov/remove-smartanswers-scoped-css

Remove smart answers scoped styles from static
Add __canary__ for checking availability

Before we serve assets from a separate CDN than the rest of GOV.UK, we need
to ensure we have a way to monitor availability. For GOV.UK, we monitor from
nine different locations around the world. We should follow this pattern for
serving assets.

On GOV.UK, we use __canary__, which is an app which responds a bit like a
GOV.UK app would do. It isn't cached at the CDN level, so the response comes
directly from origin. For assets, this was considered too heavyweight, so
the workaround was to create a text file which we can check for the
inclusion of a string within. Nimsoft doesn't allow us to check for a HTTP
response code, which isn't too great.

This commit adds that file.
Merge pull request #476 from alphagov/add-canary

Add __canary__ for checking availability
__canary__ is now in Puppet

Since https://github.gds/gds/puppet/pull/2288, the __canary__ has been in
the Nginx configuration in Puppet. We don't need this file as well as that
one, as the Nginx configuration is serving the content (and setting it to be
JSON, much like the __canary__ on GOV.UK).

Removes the file to avoid confusion. Cc: @dancarley
Merge pull request #477 from alphagov/remove-canary

__canary__ is now in Puppet
Optimises PNGs
Merge pull request #478 from alxndrsn/optimise_pngs

Optimises PNGs
Add image_optim gem
Run all of app/assets through image_optim
Updates README and CONTRIBUTING ref image optimisation
Merge pull request #479 from alxndrsn/image_optim

Image optim
Make image_optim development group only

We don't need this Gem to compile assets, it's for convenience only.
Merge pull request #480 from alphagov/make-image-optim-development-group

Make image_optim development group only
Move global rpint styles to static.

• Hide breadcrumbs
• fix cross browser exclamamtion mark for info-notice and help-notice