documentation

Pull request #1841: feature/DEV-2666-7.0-D. Improved Pie Chart widget.

Merge in WEB/documentation from feature/DEV-2666-7.0-D to release/7.0

* commit 'f03b4da458c21219666284462c2948fc81ee26da':
  [DEV-2666] refined wording and formatting
  [DEV-2666] updated images
  [DEV-2666] improved Pie Chart widget