Bugfix: Context for dates in SideBar

We fixed dates in sidebar file info having no context.
The sidebar is either showing the last modification date or the deletion date.
Before this change it wasn't obvious what kind of date was showing. Especially
when the file list was showing a completely different date (e.g., a share date)
it was confusing to the user to see a possibly different date here without explanation.

https://github.com/owncloud/web/issues/5068
https://github.com/owncloud/web/pull/6119
