Fix update mail templates

src/mail_templates/app_update_available.ejs

@@ -2,13 +2,14 @@
 
 Dear Cloudron Admin,
 
-a new version <%= updateInfo.manifest.version %> of the app '<%= app.manifest.title %>' installed at <%= app.fqdn %> is available!
-
-The app will update automatically tonight. Alternately, update immediately at <%= webadminUrl %>.
+A new version <%= updateInfo.manifest.version %> of the app '<%= app.manifest.title %>' installed at <%= app.fqdn %> is available!
 
 Changes:
 <%= updateInfo.manifest.changelog %>
 
+<% if (!hasSubscription) { -%>
+*Keep your Cloudron automatically up-to-date and secure by upgrading to a paid plan at* <%= webadminUrl %>/#/settings
+<% } -%>
 
 Powered by https://cloudron.io
 
@@ -16,4 +17,35 @@ Sent at: <%= new Date().toUTCString() %>
 
 <% } else { %>
 
+    <center>
+
+    <img src="<%= cloudronAvatarUrl %>" width="128px" height="128px"/>
+
+    <h3>Dear <%= cloudronName %> Admin,</h3>
+
+    <div style="width: 650px; text-align: left;">
+        <p>
+            A new version <%= updateInfo.manifest.version %> of the app '<%= app.manifest.title %>' installed at <%= app.fqdn %> is available!
+        </p>
+
+        <h5>Changelog:</h5>
+        <%- changelogHTML %>
+
+        <br/>
+
+        <% if (!hasSubscription) { %>
+        <p>Keep your Cloudron automatically up-to-date and secure by upgrading to a <a href="<%= webadminUrl %>/#/settings">paid plan</a>.</p>
+        <% } %>
+
+        <br/>
+    </div>
+
+    <div style="font-size: 10px; color: #333333; background: #ffffff;">
+        Powered by <a href="https://cloudron.io">Cloudron</a>.
+    </div>
+
+    </center>
+
+    <img src="https://analytics.cloudron.io/piwik.php?idsite=2&rec=1&e_c=CloudronEmail&e_a=update" style="border:0" alt="" />
+
 <% } %>