[AIRFLOW-2431] Add the navigation bar color parameter for RBAC UI

Closes #3326 from jgao54/navbar-color

airflow/www_rbac/app.py

@@ -147,6 +147,7 @@ def create_app(config=None, testing=False, app_name="Airflow"):
         def jinja_globals():
             return {
                 'hostname': socket.getfqdn(),
+                'navbar_color': conf.get('webserver', 'NAVBAR_COLOR'),
             }
 
         @app.teardown_appcontext

airflow/www_rbac/templates/appbuilder/navbar.html

@@ -18,7 +18,7 @@
 {% set menu = appbuilder.menu %}
 {% set languages = appbuilder.languages %}
 
-<div class="navbar navbar-inverse navbar-fixed-top {{menu.extra_classes}}" role="navigation">
+<div class="navbar navbar-inverse navbar-fixed-top {{menu.extra_classes}}" role="navigation" style="background-color: {{ navbar_color }};">
    <div class="container">
         <div class="navbar-header">
             <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse">