Bugfix for taxon autocomplete js

This is currently broken for applications using rails i18n and passing the locale param in the url. In these cases the request url will result in something like:

http://karnov.dk:3001/shop/admin/taxons/search.json?locale=da?ids=824,829,833,1614,1551,1595

Instead we need to use the & param separator if there is already params in the url. I have done this manually. A more elegant fix might be to use something like https://github.com/railsware/js-routes (rather than using /spree/core/app/views/spree/admin/shared/_routes.html.erb) that allows us to pass the ids in to a js routes object.