Update CHANGELOG for version 1.16.4 release date

Updated the release date for version 1.16.4 and added a note about the new option to block non-administrative session leaders from accessing encrypted box data.

Update CHANGELOG.md

Update CHANGELOG.md

Update CHANGELOG.md

Update CHANGELOG.md

Update CHANGELOG.md

Update CHANGELOG.md

Update CHANGELOG.md

Update CHANGELOG.md

Update CHANGELOG.md