Update Web UI documentation with Web UI 9.2 new features and improvements

The version of Web UI that comes with Nuxeo Platform 9.2 includes several new features and improvements. Most of them were implemented in Web UI 1.0, targetting Nuxeo Platform LTS 2016, and the Web UI documentation is already updated in 8.10. These changes should be ported on the web-ui-1.0 branch of the Web UI documentation, if not already present, and then merged on the master branch.

• Audit menu in Administration: https://github.com/nuxeo/doc.nuxeo.com-content/commit/135eb5e52cf785a60e0ca0032f326bff91d63661#diff-6a8d2f6057522cfa5642d1bb4f4ca23f

• Collections: https://github.com/nuxeo/doc.nuxeo.com-content/commit/135eb5e52cf785a60e0ca0032f326bff91d63661#diff-476dad385a4853943046212925801c65

• Workflow: https://github.com/nuxeo/doc.nuxeo.com-content/commit/135eb5e52cf785a60e0ca0032f326bff91d63661#diff-0d0ebfa7f5730045b69f8fbac50b073f

• Search higlights to be added on https://doc.nuxeo.com/userdoc/search/

• Update video screenshots to show storyboard

+ check possible other new features.