- Removed links to the gov uk stylesheets

- Deleted /stylesheets folder
- Removed sass build from gulpfile
- Changed gov links to usa links
- Changed other govuk styles, like breadcrumbs
- Changed name of uk_components file to us_components
- Fixed a few tests that broke on account of the changes

app/templates/error/401.html

@@ -4,6 +4,6 @@
   <div class="govuk-grid-row">
     <div class="govuk-grid-column-two-thirds">
     <h1>You’re not authorised to see this page</h1>
-      <p class="govuk-body"><a class="govuk-link govuk-link--no-visited-state" href="{{ url_for('main.sign_in' )}}">Sign in</a> to Notify.gov and try again.</p>
+      <p class="govuk-body"><a class="usa-link" href="{{ url_for('main.sign_in' )}}">Sign in</a> to Notify.gov and try again.</p>
   </div>
 {% endblock %}