Add two HMRC protypes

- Remove the sha from the whitehall CSS so it is always the latest and
  greatest.

_includes/_head.static.preview.html

@@ -25,7 +25,7 @@
 <meta property="og:image" content="https://assets.digital.cabinet-office.gov.uk/static/opengraph-image-85fc698c83c77d8d8cb5467a44cc12a5.png">
 <!--[if gt IE 8]><!--><link href="https://assets.digital.cabinet-office.gov.uk/static/header-footer-only-fb51c3531872f50ce5e9ce3b3e7a2b75.css" media="screen" rel="stylesheet" type="text/css">
 <!--<![endif]--><!--[if IE 6]><link href="https://assets.digital.cabinet-office.gov.uk/static/header-footer-only-ie6-72d6de0e51d55626175adcdd0cb0a183.css" media="screen" rel="stylesheet" type="text/css" /><![endif]--><!--[if IE 7]><link href="https://assets.digital.cabinet-office.gov.uk/static/header-footer-only-ie7-4cc348c67a431599746c4fa0ac00a031.css" media="screen" rel="stylesheet" type="text/css" /><![endif]--><!--[if IE 8]><link href="https://assets.digital.cabinet-office.gov.uk/static/header-footer-only-ie8-aaaa96551d81abc1cfa26e29efe7c246.css" media="screen" rel="stylesheet" type="text/css" /><![endif]--><link href="https://assets.digital.cabinet-office.gov.uk/static/print-7bad901b32df5344e949e8b2365568ce.css" media="print" rel="stylesheet" type="text/css">
-<!--[if gt IE 8]><!--><link href="https://assets.digital.cabinet-office.gov.uk/government/assets/frontend/base-7cc6291ee6fcd58479196f2fa2787dea.css" media="screen" rel="stylesheet" type="text/css">
+<!--[if gt IE 8]><!--><link href="https://assets.digital.cabinet-office.gov.uk/government/assets/frontend/base.css" media="screen" rel="stylesheet" type="text/css">
 <!--<![endif]--><link href="https://assets.digital.cabinet-office.gov.uk/government/assets/frontend/print-48357c1b450ddcf4d47b3f66caad2748.css" media="print" rel="stylesheet" type="text/css">
 <link href="https://www.gov.uk/government/feed" rel="alternate" title="Recent updates" type="application/atom+xml">
 <link href="https://www.gov.uk/api/organisations" rel="alternate" type="application/json">