Implement alert flashing from javascript

JIRA INFRA-545

app/static/js/csentry.js

+function flash_alert(message, category) {
+  var htmlString = '<div class="alert alert-' + category + ' alert-dismissible" role="alert">'
+  htmlString += '<button type="button" class="close" data-dismiss="alert" aria-label="Close">'
+  htmlString += '<span aria-hidden="true">&times;</span></button>' + message + '</div>'
+  $(htmlString).prependTo("#mainContent").hide().slideDown();
+}
+
+function remove_alerts() {
+  $(".alert").slideUp("normal", function() {
+    $(this).remove();
+  });
+}
+
 // Function to dynamically update a select field
 function update_selectfield(field_id, data, selected_value) {
   var $field = $(field_id);

app/templates/base-fluid.html

@@ -34,7 +34,7 @@
       </div>
     </div>
 
-    <div class="col-12 col-md-10 col-xl-10">
+    <div class="col-12 col-md-10 col-xl-10" id="mainContent">
       {{flashed_messages(messages, container=False, dismissible=True)}}
       {% block main %}{% endblock %}
     </div>

app/templates/base.html

@@ -54,7 +54,7 @@
 {% endblock %}
 
 {% block content %}
-  <div class="container">
+  <div class="container" id="mainContent">
     {{flashed_messages(messages, container=False, dismissible=True)}}
     {% block main %}{% endblock %}
   </div>