comments: cleanup of PR versions/author tags.

comment-history: fixes/ui changes - show explicit version conflicts - use new select2 based dropdown with nicer formatting - enabled editing of content for TODO comments

comments: save modification date for main comment on edit.

comment-history: block viewing any comment history by narrowing to specific repository which we already have permissions to.

comments: fixed links/actions

comment-history: UI fixes

comments: updated edit message when body is still the same.

swal: changed to dedicated version without animation

comments: edit functionality added

commits: detect missing commits on diffsets from new PR ancestor logic. - this would not crash the server and allow people to update some old PRs - fixes #5622