documentation

Pull request #1596: feature/ZBXNEXT-8496-7.0-D-API. Time periods for item & tophosts widget (API).

Merge in WEB/documentation from feature/ZBXNEXT-8496-7.0-D-API to release/7.0

* commit '08e74312ddd163838418733f7acd911cf8bd0135':
  [DEV-3099] Refined notes on parameter behavior for Dashboard widget (Item value) fields
  [ZBXNEXT-8496] Removed unnecessary entry
  [ZBXNEXT-8496] Removed duplicate parameter; refined parameter order
  [ZBXNEXT-8496] Time periods for item & tophosts widget (API)
  [ZBXNEXT-8496] Updated aggregate_function parameter value from "none" to "not used"
  [ZBXNEXT-8496] Time periods for item & tophosts widget (API)