Separate "server" entry

[Dantevg]

(from Unkn0wn3636 at the spigotmc WebStats thread)

Feature

For non-player-specific placeholders, display them on a separate row for the server itself, instead of displaying them for every player.

Implementation

Maybe add a separate global-placeholders config entry. All placeholders specified there will not be displayed on individual players' rows but on the server's own row.