Fixes #1185 - While connecting to the server, application becomes almost

inaccessible.

In stand (without threaded) mode, flask application is not able to
process more than one request at a time. Hence - even the client
(browser) send multiple request, when connecting the server (which is
inaccessible), rest of operations get blocked, as making the connection
with the database server is blocking operation.

In order to fix the issue, we're starting the application with thread
support, in which it will create a separate thread of each request.

web/config.py

@@ -241,6 +241,11 @@ STORAGE_DIR = os.path.join(
     'storage'
     )
 
+##########################################################################
+# Allows flask application to response to the each request asynchronously
+##########################################################################
+THREADED_MODE = True
+
 ##########################################################################
 # Local config settings
 ##########################################################################

web/pgAdmin4.py

@@ -71,8 +71,11 @@ else:
     server_port = config.DEFAULT_SERVER_PORT
 
 try:
-    app.run(host=config.DEFAULT_SERVER,
+    app.run(
+        host=config.DEFAULT_SERVER,
         port=server_port,
-        use_reloader=(config.SERVER_MODE and app.debug))
+        use_reloader=(config.SERVER_MODE and app.debug),
+        threaded=config.THREADED_MODE
+    )
 except IOError:
     app.logger.error("Error starting the app server: %s", sys.exc_info())