Validate title for custom inventories. Fixes BUKKIT-4616, BUKKIT-4663

Custom inventories currently do not validate the titles provided. Null values
cause NPEs when writing packets. Values longer than 32 characters
disconnect clients.

This change throws and IllegalArgumentException for null titles or titles
longer than 32 characters.
Add BukkitObjectIOStream tests on top of ItemMeta tests
Fix javac workaround in ItemStackTest