Update integration tests for subdomain routing.
Switch to subdomain based routing.

In order to host this on *.service.gov.uk
Redirect unknown transaction hosts to www.gov.uk
Redirect GETs to the confirm path back to the start.

This URL only reqponds to POST requests.
Don't use a separate asset-host

In preparation for moving this away from depending on static
Remove redundant controller actions and view
Remove unused application.css
Switch to run under www.*.service.gov.uk

To bring in line with the service manual guidance
(https://www.gov.uk/service-manual/operations/operating-servicegovuk-subdomains.html).
Also changes the start page to be at /start, as / will be a redirect
back to the www.gov.uk start page.
Redirect / to the start page on www.gov.uk
Remove some redundant controller stuff.
Disallow spidering in robots.txt

As per https://www.gov.uk/service-manual/operations/operating-servicegovuk-subdomains.html#robotstxt-and-root-level-redirections
Add healthcheck endpoint
Merge pull request #1 from alphagov/subdomain_routing

Switch to subdomain based routing.