[Python 3 compatibility] Introduced a separate HTML safe string function

in 'utils' module, earlier the function -'escape(...)' was converting
the strings to bytes, and that's reason, it was not working on Python 3.

web/pgadmin/utils/html.py

@@ -0,0 +1,18 @@
+##########################################################################
+#
+# pgAdmin 4 - PostgreSQL Tools
+#
+# Copyright (C) 2013 - 2016, The pgAdmin Development Team
+# This software is released under the PostgreSQL Licence
+#
+#########################################################################
+
+"""Utilities for HTML"""
+
+import cgi
+
+
+def safe_str(x):
+    return cgi.escape(x).encode(
+        'ascii', 'xmlcharrefreplace'
+    ).decode()