Add guava to pom
Fix bug in PermissionSign, TeleportSign and RepairSign where they would skip some checks if the sign is free
Fix HealSign after Bukkit updates for 1.6.1
Use ImmutableMap in TeleportSign
Add EnchantSign and UnsafeEnchantSign
Merge branch 'master' of https://github.com/Philipp15b/MagicSigns