Add some visual differentiation for null info

We use light grey for stuff like ‘not set’ elsewhere. This knocks it
back a bit so the actual information on the page is more prominent.

app/templates/views/find-users/user-information.html

@@ -12,7 +12,7 @@
         {{ user.name }}
       </h1>
       <p>{{ user.email_address }}</p>
-      <p>{{ user.mobile_number }}</p>
+      <p class="{{ '' if user.mobile_number else 'hint' }}">{{ user.mobile_number or 'No mobile number'}}</p>
       <h2 class="heading-medium">Live services</h2>
       <nav class="browse-list">
         {% if user.live_services %}
@@ -47,7 +47,7 @@
       </nav>
       <h2 class="heading-medium">Last login</h2>
       {% if not user.logged_in_at %}
-      <p>This person has never logged in</p>
+      <p class="hint">This person has never logged in</p>
       {% else %}
       <p>Last logged in
         <time class="timeago" datetime="{{ user.logged_in_at }}">