Add "static file" configuration to eb task

[tdesposito]

Add options to configure eb proxy to set the location/href of static files:

The config should look like:

{
  "extensions": {
    "static_files": {
      "/static": "static",
      "/html": "htmldocs",
    }
  }
}

The result in the .ebextensions/60-devpail-options.config file should be of the form:

aws:elasticbeanstalk:environment:proxy:staticfiles:
    /static: static
    /html: htmldocs