Improve error message for bad templates when using cordova create --template

right now, we don't handle the error very well when you are using a invalid template during cordova create --template sometemplate. We just spew out the npm stack. It would be better if we could catch the error and provide a nicer message to our users. Something along the lines of the template is invalid. Make sure you follow the template guide when creating a template. (link to template guide). Templates now require a package.json.