Importing from an RSS feed. 

I choose this branch because it has the lookup field. That is a feature that really needs to be integrated into the primary rails_admin repo. But I figured I'd start here and work my way back. (This is my first pull request, BTW)
I've added the ability to import your data from an RSS feed. You can configure the mapping in the configuration file. Currently, if you input a url, it's assumed that the file is an RSS feed. However, you really should be able to open a CSV file from a URL, not just an uploaded file. 
I also futzed around with the view.