Add support for creating dialogs, and add an About dialog.

This adds bootstrap-dialog to help with creation of nice dialogs,
and adds the ability for modules to render Javascript into the
browser, and specify onclick handlers in the menu system.

Also add a basic About dialog, using the new infrastructure and
showing some useful info about the application.

web/pgadmin/templates/base.html

@@ -15,6 +15,7 @@
         <meta name="dcterms.dateCopyrighted" content="2014 - 2015">
 
         <link rel="stylesheet" href="{{ url_for('static', filename='css/bootstrap.min.css') }}">
+        <link rel="stylesheet" href="{{ url_for('static', filename='css/bootstrap-dialog.min.css') }}">
         <style>
             body {
                 padding-top: 50px;
@@ -36,6 +37,7 @@
 
         <script src="{{ url_for('static', filename='js/vendor/jquery-1.11.1.min.js') }}"></script>
         <script src="{{ url_for('static', filename='js/vendor/bootstrap.min.js') }}"></script>
+        <script src="{{ url_for('static', filename='js/vendor/bootstrap-dialog.min.js') }}"></script>
         <script src="{{ url_for('static', filename='js/main.js') }}"></script>
     </body>
 </html>

web/pgadmin/templates/security/watermark.html

@@ -1,5 +1,5 @@
 {% block watermark %}
 <div style="position: fixed; bottom: 0; right: 0;">
-    <img src="img/logo-right-256.png" alt="pgAdmin 4">
+    <img src="{{ url_for('static', filename='img/logo-right-256.png') }}" alt="pgAdmin 4">
 </div>
 {% endblock %}