- 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/partials/check/not-allowed-to-send-to.html

@@ -7,6 +7,6 @@
   {%- endif %}
 </h1>
 <p class="govuk-body">
-  In <a class="govuk-link govuk-link--no-visited-state" href="{{ url_for('.trial_mode_new') }}">trial mode</a> you can only
+  In <a class="usa-link" href="{{ url_for('.trial_mode_new') }}">trial mode</a> you can only
   send to yourself and members of your team
 </p>