Sign name override for server-plot flag, and og owner display

There is some request for the "server-plot" flag to override the display name on the plot's sign.
This change, if included, should also include some method for P2 admins / server ops to see the "legitimate" plot owner, if there is any actually need to do so - such as the plot potentially being removed if the plot owner is banned, for example. If the server-plot flag would override anything like that, then displaying the original owner's name may not be needed. I think at that point, the plot would "legitimately" be owned by "server" - which itself would take care of all displayed owner fields. shrug

Just more to chew on.

Being as this is a feature request, and not a bug, as originally reported at https://github.com/IntellectualSites/PlotSquared/issues/2430 - that ticket has been closed and this opened so that the devs can focus on actual bugs.

Start by reviewing how the server-plot flag controls plot sign display and compare this request with the closed issue #2430. Clarify whether server operators need to see the original owner and decide how server-owned plots should appear. Done means the requested display-name override and owner visibility behavior are specified and implemented.