documentation

Pull request #1836: feature/ZBXNEXT-8956-7.0-D2. Refined widget communication framework documentation.

Merge in WEB/documentation from feature/ZBXNEXT-8956-7.0-D2 to release/7.0

* commit 'cdc2b7cf3d902bc171b8296fe228b5e5691f4cc2':
  [ZBXNEXT-8956] updated image size
  [ZBXNEXT-8956] updated "What's new" with changes to Map & Graph widgets
  [ZBXNEXT-8956] refined wording and formatting
  [ZBXNEXT-8956] clarified widget behavior (prev. "Widget states")
  [ZBXNEXT-8956] clarified "Time period" configuration behavior
  [ZBXNEXT-8956] refined "Widget states" section