Add pages for create/view/revoke API keys

Copying what they’ve done on GOV.UK Pay, we should let users:
- generate as many keys as they want
- only see the key at time of creation
- give keys a name
- revoke any key at any time (this should be a one way operation)

And based on discussions with @minglis and @servingUpAces, the keys should be
used in conjunction with some kind of service ID, which gets encrypted with the
key. In other words the secret itself never gets sent over the wire.

This commit adds the UI (but not the underlying API integration) for doing the
above.

app/templates/views/api-keys/create.html

@@ -0,0 +1,24 @@
+{% extends "withnav_template.html" %}
+{% from "components/page-footer.html" import page_footer %}
+{% from "components/textbox.html" import textbox %}
+
+{% block page_title %}
+  GOV.UK Notify | API keys and documentation
+{% endblock %}
+
+{% block maincolumn_content %}
+
+  <h1 class="heading-xlarge">
+    Add a new API key
+  </h1>
+
+  <form method="post">
+    {{ textbox(key_name, hint='eg CRM application') }}
+    {{ page_footer(
+      'Continue',
+      back_link=url_for('.api_keys', service_id=service_id),
+      back_link_text='Back to API keys'
+    ) }}
+  </form>
+
+{% endblock %}

app/templates/views/api-keys/revoke.html

@@ -0,0 +1,37 @@
+{% extends "withnav_template.html" %}
+{% from "components/page-footer.html" import page_footer %}
+{% from "components/api-key.html" import api_key %}
+
+{% block page_title %}
+  GOV.UK Notify | API keys and documentation
+{% endblock %}
+
+{% block maincolumn_content %}
+
+    <div class="grid-row">
+      <div class="column-two-thirds">
+
+        <h1 class="heading-xlarge">
+          Revoke API key
+        </h1>
+
+        <p>
+          ‘Test key 1’ will no longer let you connect to GOV.UK Notify.
+        </p>
+        <p>
+          You can’t undo this.
+        </p>
+
+      </div>
+    </div>
+
+    <form method="post">
+      {{ page_footer(
+        'Revoke this API key',
+        back_link=url_for('.api_keys', service_id=service_id),
+        back_link_text='Back to API keys',
+        destructive=True
+      ) }}
+    </form>
+
+{% endblock %}

app/templates/views/api-keys/show.html

@@ -0,0 +1,33 @@
+{% extends "withnav_template.html" %}
+{% from "components/page-footer.html" import page_footer %}
+{% from "components/api-key.html" import api_key %}
+
+{% block page_title %}
+  GOV.UK Notify | API keys and documentation
+{% endblock %}
+
+{% block maincolumn_content %}
+
+    <div class="grid-row">
+      <div class="column-two-thirds">
+
+        <h1 class="heading-xlarge">
+          New API key
+        </h1>
+
+        <p>
+          Copy your key to somewhere safe. You won’t be able to see it again
+          once you leave this page.
+        </p>
+
+        {{ api_key('d30512af92e1386d63b90e5973b49a10', 'CRM application') }}
+
+      </div>
+    </div>
+
+    {{ page_footer(
+      back_link=url_for('.api_keys', service_id=service_id),
+      back_link_text='Back to API keys'
+    ) }}
+
+{% endblock %}