[enh] configurable listening http protocol version

searx/settings.yml

     secret_key : "ultrasecretkey" # change this!
     base_url : False # Set custom base_url. Possible values: False or "https://your.custom.host/location/"
     image_proxy : False # Proxying image results through searx
+    http_protocol_version : "1.0"  # 1.0 and 1.1 are supported
 
 ui:
     themes_path : "" # Custom ui themes path - leave it blank if you didn't change

searx/webapp.py

 
 # serve pages with HTTP/1.1
 from werkzeug.serving import WSGIRequestHandler
-WSGIRequestHandler.protocol_version = "HTTP/1.1"
+WSGIRequestHandler.protocol_version = "HTTP/{}".format(settings['server']['http_protocol_version'])
 
 static_path, templates_path, themes =\
     get_themes(settings['ui']['themes_path']