Updating site to use USWDS styles (#509)

* Updated header and footer
* Updated fonts
* Moved files around and updated gulpfile to correct the build process when it goes to production
* Adjusted grid templating
* Added images to assets
* Update app/templates/components/uk_components/footer/template.njk

Co-authored-by: Steven Reilly <stvnrlly@users.noreply.github.com>

app/templates/views/user-profile/security-keys.html

@@ -51,7 +51,7 @@
       "classes": "banner-dangerous govuk-!-display-none",
       "html": (
         'There’s a problem with your security key' +
-        '<p class="govuk-body">Check you have the right key and try again. ' +
+        '<p>Check you have the right key and try again. ' +
         'If this does not work, ' +
         '<a class="govuk-link govuk-link--no-visited-state" href=' + url_for('main.support') + ">contact us</a>." +
         '</p>'
@@ -88,11 +88,11 @@
     {% else %}
       <div class="govuk-grid-column-one-half">
         {{ page_header(page_title) }}
-        <p class="govuk-body">
+        <p>
           Security keys are an alternative way of signing in to Notify,
           instead of getting a code in a text message
         </p>
-        <p class="govuk-body">
+        <p>
           You can buy any key that’s compatible with the WebAuthn
           standard.
         </p>