[C+B] Implement command tab completion in the console. Adds BUKKIT-4168

##### The Issue:
Even though Minecraft provides ingame command tab completion for a few version already, but there is still no tab completion for server admins in the console.

##### Justification for this PR:
Command tab completion in the console really improves the "console experience" for admins, as it can prevent typos and generelly speeds up the command usage.

##### PR Breakdown:
This PR implements the Completer interface provided by JLine to. This completer simply calls CommandMap.tabCompleter(CommandSender, String). Registration of the completer is done in the constructor of PlayerList right after the CraftServer and the ConsoleCommandSender have been created.
 
##### Testing Results and Materials:
Testing this is straight forward: Enter something (or nothing) into the console and press tab, it works pretty much exactly like the ingame completion
 
B-868 - https://github.com/Bukkit/Bukkit/pull/868 - Command(Map) changes to allow console tab completion
CB-1151 - https://github.com/Bukkit/CraftBukkit/pull/1151 - Completer implementation
 
##### JIRA Ticket: 
BUKKIT-4168- https://bukkit.atlassian.net/browse/BUKKIT-4168