Add support for an unmapped fields token

Problem/Motivation

This is an amazing module, it really opens up a lot of really cool applications for Drupal and webforms, many thanks for your work on it!

I have an interesting application in which I am looking at using this module to take several different webforms and map them into a single content-type. Some of the fields on the webforms will be common and map directly into fields on my content-type. For the other fields that are unmapped I would like to just place them into the node body.

Currently, I can use the [webform_submission:values] token to put all the fields into the node body, which would create duplicate information on node view. Or I can put each individual submission value token into the node body for each form but that is a bit painful to manage. So.... I was thinking that is would be great of there was a token that does exactly what the [webform_submission:values] token does EXCEPT that it excludes any fields that are currently mapped via webform content creator.

Proposed resolution

Create a token [webform_submission:unmapped_values] that outputs all of the submission values that are not mapped to fields in the content-type.