[B] Improve functionality of white-list command - Fixes BUKKIT-5358

Notice: The ticket report is filed as "Bug" instead of "Improvement"

**The Issue:**
I believe the white-list command could be improved in a few ways (as described below).

**Changes**
 - Fixed: Grammar on sentences.
  * Added full stops onto the end of sentences.
 - Added: *white-list status* command (No way to check in-game)
  * Tell the sender if the white-list is enabled or not.
 - Added: Aliases of sub commands (Ease of Use, **First letters of each sub command**)
  * */whitelist on* Aliases: enable, e
  * */whitelist off* Aliases: disable, o
  * */whitelist status* Aliases: s
  * */whitelist list* Aliases: l, who
 - Added: Player count to *white-list list* (Functionality)
  * *Example:* "White-listed players (1): stuntguy3000"
 - Fixed: Player is told when no players are on the white-list, instead of an empty list. (Ease of Use)
  * *Message:* "No players have been white-listed."

**Justification for this PR:**
The changes were made because I feel they help to improve ease of use with the command, and overall functionality.

**JIRA Ticket:**
https://bukkit.atlassian.net/browse/BUKKIT-5358

**Testing Material**
Compiled changes from local fork and tested.

Associated Bukkit Ticket: https://github.com/Bukkit/Bukkit/pull/1021