[vcs-log] user-filter: treat empty user name as no filter.
getItem returns Item typed object +review
continue WEB-2093: up/down/add/remove actions
overrides
mac file chooser must respect FileChooserDescriptor.isFileSelectable +review

Client can override isFileSelectable, but mac file chooser doesn't support complex selection logic, so, we should perform post-check.
cleanup, reuse getItem
continue WEB-2093: fix editing
Cleanup (typo)
allow external documentation over references with multiple resolve