documentation

Pull request #1408: feature/ZBXNEXT-8145-7.0-D-API. Communication framework for widgets (API).

Merge in WEB/documentation from feature/ZBXNEXT-8145-7.0-D-API to release/7.0

* commit 'e9ead40e855489fbe92bb6779680e4f2edafd4db':
  [ZBXNEXT-8145] Refined Dashboard API entries
  [ZBXNEXT-8145] Refined Dashboard API entries
  [ZBXNEXT-8145] Communication framework for widgets (API)
  [ZBXNEXT-8145] Props referring to DB objects updated to array format
  [ZBXNEXT-8145] Updated *Map* and *Map navigation tree* widgets
  [ZBXNEXT-8145] *Override host* not available on template dashboard
  [ZBXNEXT-8145] Reworded time period parameters
  [ZBXNEXT-8145] Communication framework for widgets (API)
  [ZBXNEXT-8145] updated time period fields