Added health display for mobs during combat.

During combat, players will now see a healthbar appear over the head of
hostile mobs when they are damaged. This healthbar will have two display
options - HEARTS and BAR - which can be changed via the /mobhealth
command.

New Permissions:
mcmmo.mobhealthdisplay - Allows viewing of mob health display
mcmmo.commands.mobhealth - Allows access to the /mobhealth command

New Config Options (config.yml):
Mob_Healthbar.Display_Type - the default health display type
Mob_Healthbar.Display_Time - the amount of time to show health display

src/main/java/com/gmail/nossr50/commands/MobhealthCommand.java

@@ -0,0 +1,39 @@
+package com.gmail.nossr50.commands;
+
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandExecutor;
+import org.bukkit.command.CommandSender;
+
+import com.gmail.nossr50.datatypes.MobHealthbarType;
+import com.gmail.nossr50.datatypes.player.PlayerProfile;
+import com.gmail.nossr50.util.commands.CommandUtils;
+import com.gmail.nossr50.util.player.UserManager;
+
+public class MobhealthCommand implements CommandExecutor {
+
+    @Override
+    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
+        if (CommandUtils.noConsoleUsage(sender)) {
+            return true;
+        }
+
+        switch (args.length) {
+            case 1:
+                PlayerProfile playerProfile = UserManager.getPlayer(sender.getName()).getProfile();
+
+                try {
+                    MobHealthbarType type = MobHealthbarType.valueOf(args[0].toUpperCase().trim());
+                    playerProfile.setMobHealthbarType(type);
+                    sender.sendMessage("Display type changed to: " + type); //TODO: Localize
+                    return true;
+                }
+                catch (IllegalArgumentException ex) {
+                    sender.sendMessage("Invalid type!"); //TODO: Localize
+                    return true;
+                }
+
+            default:
+                return false;
+        }
+    }
+}