- 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/components/big-number.html

@@ -1,6 +1,6 @@
 {% macro big_number(number, label, link=None, currency='', smaller=False, smallest=False) %}
   {% if link %}
-    <a class="usa-link govuk-link--no-visited-state display-block margin-bottom-1" href="{{ link }}">
+    <a class="usa-link display-block margin-bottom-1" href="{{ link }}">
   {% endif %}
       <span class="big-number{% if smaller %}-smaller{% endif %}{% if smallest %}-smallest{% endif %}">
         <span class="big-number-number">
@@ -42,7 +42,7 @@
       <span class="big-number-status{% if danger_zone %}-failing{% endif %}">
         {% if failures %}
           {% if failure_link %}
-            <a class="govuk-link govuk-link--no-visited-state" href="{{ failure_link }}">
+            <a class="usa-link" href="{{ failure_link }}">
               {{ "{:,}".format(failures) }}
               failed – {{ failure_percentage }}%
             </a>