Add an appliance templates directory

Fix https://github.com/GNS3/gns3-gui/issues/2133

conf/gns3_server.conf

@@ -11,9 +11,13 @@ certkey=/home/gns3/.config/GNS3/ssl/server.key
 
 ; Path where devices images are stored
 images_path = /home/gns3/GNS3/images
+
 ; Path where user projects are stored
 projects_path = /home/gns3/GNS3/projects
 
+; Path where user appliances are stored
+appliances_path = /home/gns3/GNS3/appliances
+
 ; Option to automatically send crash reports to the GNS3 team
 report_errors = True