[B+C] Set/get player count for client's multiplayer connect server list. Adds BUKKIT-2465

The Issue:

Actually , there is no way to set if a player is counted in the player online counts

Justification for this PR:

This PR allow a true vanish option and remove a player from the count list

PR Breakdown:

This PR implement the set and get values for counted method in the Player entity type

Relevant PR:

CraftBukkit: Bukkit/CraftBukkit#

Jira Ticket :
Leaky: https://bukkit.atlassian.net/browse/BUKKIT-2465