Replace straightforward buttons and links styled like buttons

This replaces the buttons that aren't part of a macro and that we don't
need to write additional styles for with their govuk-frontend equivalent.

There were some links that were styled to look like buttons, so these
have also been replaced with the new govuk-frontend macro.

There was one button on the `choose-account.html` template that was in a
section of code that was never reached - this has been deleted.

app/templates/views/organisations/index.html

@@ -1,7 +1,6 @@
 {% extends "withoutnav_template.html" %}
 {% from "components/live-search.html" import live_search %}
-{% from "components/page-footer.html" import page_footer %}
-{% from "components/page-header.html" import page_header %}
+{% from "components/button/macro.njk" import govukButton %}
 
 {% block per_page_title %}
   All organisations
@@ -53,7 +52,12 @@
            
         </div>
         <div class="column-three-quarters">
-          <a href="{{ url_for('main.add_organisation') }}" class="button-secondary">New organisation</a>
+          {{ govukButton({
+            "element": "a",
+            "text": "New organisation",
+            "href": url_for('main.add_organisation'),
+            "classes": "govuk-button--secondary"
+          }) }}
         </div>
       </div>
     </div>

app/templates/views/organisations/organisation/settings/preview-email-branding.html

@@ -1,5 +1,7 @@
 {% extends "org_template.html" %}
 {% from "components/form.html" import form_wrapper %}
+{% from "components/button/macro.njk" import govukButton %}
+
 {% block org_page_title %}
   Preview email branding
 {% endblock %}
@@ -14,7 +16,7 @@
         <div class="form-group">
           {{ form.hidden_tag() }}
           <div class="page-footer">
-            <button type="submit" class="button">Save</button>
+            {{ govukButton({ "text": "Save" }) }}
           </div>
         </div>
       {% endcall %}

app/templates/views/organisations/organisation/users/index.html

@@ -4,6 +4,7 @@
 {% from "components/tick-cross.html" import tick_cross %}
 {% from "components/textbox.html" import textbox %}
 {% from "components/live-search.html" import live_search %}
+{% from "components/button/macro.njk" import govukButton %}
 
 {% block org_page_title %}
   Team members
@@ -52,7 +53,12 @@
   </div>
 
   <div class="js-stick-at-bottom-when-scrolling">
-    <a href="{{ url_for('.invite_org_user', org_id=current_org.id) }}" class="button-secondary">Invite team member</a>
+    {{ govukButton({
+      "element": "a",
+      "text": "Invite team member",
+      "href": url_for('.invite_org_user', org_id=current_org.id),
+      "classes": "govuk-button--secondary"
+    }) }}
   </div>
 
 {% endblock %}