Ability to calculate the grand average of all "Review" style ratings

[lindseydiloreto]

It's possible to add a Rate field to a front-end form. Using this technique, you can create a "Reviews" section for users to rate & review your elements.

However, it's currently a little tricky (though possible) to get a grand average of all ratings associated with an element. There should be a way to pre-calculate and save this value, so that it doesn't need to be calculated at runtime.