Fix settings

Hi there!

It looks like by using get_project_settings you can only retrieve the settings in the config file.
In order to override settings like ELASTICSEARCH_INDEX from other parts of the spider (like the command line), the from_crawler method must be implemented and used to load settings.


ELASTICSEARCH_USERNAME and ELASTICSEARCH_PASSWORD shouldn't be required fields, I would say do a quick check to either pass in an empty {} or {username: input, password: input}