Allow service to set callback url for notifications

app/templates/views/api/callbacks.html

@@ -0,0 +1,49 @@
+{% extends "withnav_template.html" %}
+{% from "components/textbox.html" import textbox %}
+{% from "components/page-footer.html" import page_footer %}
+
+{% block service_page_title %}
+  Callbacks
+{% endblock %}
+
+{% block maincolumn_content %}
+  <div class="grid-row">
+    <div class="column-five-sixths">
+      <h1 class="heading-large">Callbacks</h1>
+      <p>
+        See our <a href="{{ url_for('.callbacks') }}">documentation on the format of the callback</a>.
+      </p>
+
+      <form method="post">
+        {% if can_receive_inbound %}
+          {{ textbox(
+            form.inbound_url,
+            width='1-1',
+            hint='Valid https URL'
+          ) }}
+          {{ textbox(
+            form.inbound_bearer_token,
+            width='2-3',
+            hint='At least 10 characters'
+          ) }}
+        {% endif %}
+        {{ textbox(
+          form.outbound_url,
+          width='1-1',
+          hint='Valid https URL'
+        ) }}
+        {{ textbox(
+          form.outbound_bearer_token,
+          width='2-3',
+          hint='At least 10 characters'
+        ) }}
+          {{ page_footer(
+          'Save',
+          back_link=url_for('.api_integration', service_id=current_service.id),
+          back_link_text='Back to API integration'
+      ) }}
+      </form>
+    </div>
+  </div>
+
+{% endblock %}