Adding config element for alert message in navbar (#938)

caravel/assets/stylesheets/caravel.css

@@ -202,3 +202,8 @@ div.widget .slice_container {
 .alert a:not(.close) {
   color: gray !important;
 }
+
+.navbar .alert {
+    padding: 5px 10px;
+    margin-top: 15px;
+}

caravel/bin/caravel

@@ -7,7 +7,6 @@ from __future__ import unicode_literals
 import logging
 from datetime import datetime
 from subprocess import Popen
-import textwrap
 
 from flask_migrate import MigrateCommand
 from flask_script import Manager

caravel/config.py

@@ -180,6 +180,11 @@ BACKUP_COUNT = 30
 # Set this API key to enable Mapbox visualizations
 MAPBOX_API_KEY = ""
 
+# If defined, shows this text in an alert-warning box in the navbar
+# one example use case may be "STAGING" to make it clear that this is
+# not the production version of the site.
+WARNING_MSG = None
+
 
 try:
     from caravel_config import *  # noqa

caravel/templates/appbuilder/navbar.html

@@ -18,6 +18,14 @@
         {% include 'appbuilder/navbar_menu.html' %}
       </ul>
       <ul class="nav navbar-nav navbar-right">
+        {% set WARNING_MSG = appbuilder.app.config.get('WARNING_MSG') %}
+        {% if WARNING_MSG %}
+          <li>
+            <div class="alert alert-danger" role="alert">
+              {{ WARNING_MSG | safe }}
+            </div>
+          </li>
+        {% endif %}
         <li><a href="https://github.com/airbnb/caravel" title="Caravel's Github">
           <i class="fa fa-github fa-lg"></i></a>
         </li>