Export total ratings

[rafaehlers]

The idea is to have the possibility to include the information provided by these Merge Tags: https://docs.gravitykit.com/article/1012-ratings-reviews-merge-tags

[rafaehlers]

https://secure.helpscout.net/conversation/2607406844/54744, https://secure.helpscout.net/conversation/2662452647/56160 (same user: Craig Davis)