documentation

Pull request #1785: feature/ZBXNEXT-8686-7.0-D. Added Item navigator widget.

Merge in WEB/documentation from feature/ZBXNEXT-8686-7.0-D to release/7.0

* commit 'f5a02b9c51034fcaf65944ccb07500469d47b8e4':
  [ZBXNEXT-8686] renamed "host/item pattern" to "host/item patterns"
  [ZBXNEXT-8686] fixed shortcomings
  [ZBXNEXT-8686] updated wording (controlling → to control)
  [ZBXNEXT-8686] clarified tags-related parameter description
  [ZBXNEXT-8686] clarified Item/Host limit parameter behavior
  [ZBXNEXT-8686] added temporary note on limited feature availability
  [ZBXNEXT-8686] merged Host navigator and Item navigator "What's new" entries
  [ZBXNEXT-8686] added Item navigator widget
  [ZBXNEXT-8686] copied host_navigator.md as a template for item_navigator.md