[fix] save unknown preferences parameters to cookies

Without this courgette color selector can not work

searx/preferences.py

 
         self.engines = EnginesSetting('engines', choices=engines)
         self.plugins = PluginsSetting('plugins', choices=plugins)
+        self.unknown_params = {}
 
     def parse_cookies(self, input_data):
         for user_setting_name, user_setting in input_data.iteritems():
                 enabled_categories.append(user_setting_name[len('category_'):])
             elif user_setting_name.startswith('plugin_'):
                 disabled_plugins.append(user_setting_name)
+            else:
+                self.unknown_params[user_setting_name] = user_setting
         self.key_value_settings['categories'].parse_form(enabled_categories)
         self.engines.parse_form(disabled_engines)
         self.plugins.parse_form(disabled_plugins)
             user_setting.save(user_setting_name, resp)
         self.engines.save(resp)
         self.plugins.save(resp)
+        for k, v in self.unknown_params.items():
+            resp.set_cookie(k, v, max_age=COOKIE_MAX_AGE)
         return resp