Make date format configurable

It should not be "short" by default. When talking about dates, the way to get short is to remove the time. Drupal revisions inherently *need* time because they are so chatty.

Just updated the MR to cover 2 new places where the hard coded format was used and also added a field diff plugin for date fields.

I've rebased the MR to cover the latest changes in the dev branch.