fix issue #3671 reshare a post multiple times
update changelog
fix after sign-up popups overlaping header
fix .popover overlapping header
Merge pull request #3831 from marpo60/fix-reshare

Remove the 'Reshare' link on posts if the user has already reshared the post, and displays an error in case a user tries to reshare a post they have already reshared.
Merge pull request #3834 from asphxia/3833-popups-overlap-header

Fix popovers overlapping the header topbar on scroll.