Show name of a post's editor if a post was edited

[GunChleoc]

Recently a user's post was accidentally edited by a moderator. So the idea came up to show the name of the editor: Instead

 Edited: date

we should may show:

 Edited by username: date

I think this is an act of transparency.

We may also want a 'editor comment' so the result would be:

 Edited by username: editors comment

I think showing the date can be omitted.

[GunChleoc (gunchleoc)]

Issue moved to https://github.com/widelands/widelands-website/issues/295