Delete contacts and use only from Google functionality

Hi! I added the functionality of using only the contacts in Google and delete the others that are in the phone. I know is a bit radical, but I had problems with the version of the importer in my Geeksphone Peak (it was an old version of this repo installed there) and I think this functionality might be useful for some people.

If you check the checkbox all your contacts will be deleted and it will add only your contacts in Google.

Cheers!

Javi.