added support for the import.io plugin

Another pull request for the import.io plugin. We added support for the plugin as well as the development stage. Feel free to hit me with questions if needed. 

I have 2 questions though : 
* what is the procedure for the plugin to appear there : http://www.pentaho.com/marketplace/ ?
* I can see on this page when you click on a plugin that there 2 buttons (Contact dev and live demo), are there any fields in the marketplace.xml to activate these buttons?

Thanks and regards,

Nicolas