text: Title: url parameters are not available in `dcc.Location`
  Body: we're only sending the `window.location.pathname` (https://github.com/plotly/dash-core-components/blob/master/src/components/Location.react.js#L36) but we could send an object of `window.location.search` (https://stackoverflow.com/questions/5448545/how-to-retrieve-get-parameters-from-javascript)
  
  as reported in https://community.plot.ly/t/get-url-with-get-parameters/5878/1