Added dismissable notifications

- Bootstrap alert
- Can close manually
- Also set to disappear after configurable time

InvenTree/static/script/notification.js

@@ -0,0 +1,8 @@
+function showAlert(target, message, timeout=5000) {
+
+    $(target).find(".alert-msg").html(message);
+    $(target).show();
+    $(target).delay(timeout).slideUp(200, function() {
+        $(this).alert(close);
+    });
+}