Major compatibility improvement, 1.9 support, expanded API and more

Massive code cleanup#2 -> Performance improvements
More powerful invisibility to improve compatibility with other plugins
New useful API method: boolean canSee(Player viewer, Player viewed)
Updated TrailGUI hook
Invalid hooks can no longer break SuperVanish
Removed the SilentChest feature temporarily due to missing 1.9 ProtocolLib wrappers, I'll add this feature back asap