Typehinted up entity API

Did you guys think ALPHA7 changes were done?!
Sone stuff still needs some work, most notably data-properties can't be typed yet because they are just mushed into a couple of methods.

src/pocketmine/OfflinePlayer.php

@@ -55,7 +55,7 @@ class OfflinePlayer implements IPlayer, Metadatable{
 		return $this->getPlayer() !== null;
 	}
 
-	public function getName(){
+	public function getName() : string{
 		return $this->name;
 	}