documentation

Pull request #1092: feature/ZBXNEXT-2299-7.0-D

Merge in WEB/documentation from feature/ZBXNEXT-2299-7.0-D to release/7.0

* commit 'ab2141b86ffcf84a0a384deb4e6cbec9388630d2':
  adding widget description and screenshot
  minor wording: "ever" added
  wrong text deleted
  page parameters, problems widget updated
  field name corrected
  whatsnew added
  Ack./unack. problem filter description update, screenshot update