Some plugins (e.g. older builds of EssentialsX) assume that
ServerListPingEvent.getSampleText() returns a mutable copy of
the player sample list. This was the case until it was refactored
on top of the new API introduced in #980.
As a result, they may run into an error when trying to modify the
returned list directly. Modify getSampleText() to return a mutable
copy (a plain ArrayList) to mimic the old behavior.
Don't want to risk mutating players properties in server list (unlikely, but lets be proper)
and Skull also has a setter API, so that should be used too.
