Replacing old inventory protecting with safe packet modifications using ProtocolLib.

Instead of clearing the inventory of players and storing it's contents in a file, we now prevent
the server from sending the inventory packet if the player is not logged in. The player will
see a empty inventory, but has still his items stored on the server. Therefore we don't
need to modify the player's inventory and we won't make any inventory corrupted.

Fixes Xephi/AuthMeReloaded#203,
Fixes Xephi/AuthMeReloaded#193,
Fixes Xephi/AuthMeReloaded#191,
Fixes Xephi/AuthMeReloaded#148

Remove dead code + Fix empty inventory on the unregister command

Fix NPE if ProtocolLib isn't enabled or installed

src/main/resources/plugin.yml

@@ -4,7 +4,7 @@ website: http://dev.bukkit.org/bukkit-plugins/authme-reloaded/
 description: AuthMe prevents people, which aren't logged in, from doing stuff like placing blocks, moving, typing commands or seeing the inventory of the player.
 main: fr.xephi.authme.AuthMe
 version: ${project.version}
-softdepend: [Vault, ChestShop, Multiverse-Core, Citizens, CombatTag, Essentials, EssentialsSpawn, PerWorldInventories]
+softdepend: [Vault, ChestShop, Multiverse-Core, Citizens, CombatTag, Essentials, EssentialsSpawn, PerWorldInventories, ProtocolLib]
 commands:
     register:
         description: Register an account
@@ -22,7 +22,7 @@ commands:
         usage: /logout
     unregister:
         description: unregister your account
-        usage: /unregister password         
+        usage: /unregister password
     authme:
         description: AuthMe op commands
         usage: '/authme reload|register playername password|changepassword playername password|unregister playername|version'