Update dashboard and template flow (#514)

* Updated header and footer
* Moved files around and updated gulpfile to correct the build process when it goes to production
* Updated fonts
* Adjusted grid templating
* Adding images to assets
* Updated account pages, dashboard, and pages in message sending flow
* Updated the styling for the landing pages in the account section once logged in

app/templates/views/manage-users.html

@@ -9,7 +9,7 @@
 
 {% block maincolumn_content %}
 
-  <h1 class="heading-medium">
+  <h1 class="font-body-lg">
     Team members
   </h1>
 
@@ -89,7 +89,7 @@
         "element": "a",
         "text": "Invite a team member",
         "href": url_for('.invite_user', service_id=current_service.id),
-        "classes": "govuk-button--secondary"
+        "classes": "usa-button"
       }) }}
     </div>
   {% endif %}