documentation

Pull request #1103: feature/ZBX-21883-7.0-D: [ZBX-21883] Map input element changed to multiselect; added more info on configuring the navtree widget.

Merge in WEB/documentation from feature/ZBX-21883-7.0-D to release/7.0

* commit '7cdfb71845dc507798942434e5dc25365e944037':
  [ZBX-21883] Removed a line break; updated screenshot sizes
  [ZBX-21883] Map input element changed to multiselect (updated info, screenshots); added additional info on configuring the navtree widget