Rework of the inventory system.
Recreation of hollow-cube#132

Main changes:

• Accurate click handling (except for special slots like result slots)
• Improved event API: allows accessing all click information via Click.Info, as well as providing a list of all changes via Click.Result
• Removed InventoryCondition in favor of three events: InventoryPreClickEvent, modifying only click info, like slot IDs; InventoryClickEvent, modifying the list of changes that will occur as a result of the click; and InventoryPostClickEvent, which can view all the click information but happens after handling is finished

Changes:

• Added InventoryButtonClickEvent
• Moved a lot of behaviour into AbstractInventory, renamed AbstractInventory to Inventory and Inventory to ContainerInventory
• Inventory events return the relevant PlayerInventory instead of null in #getInventory
• Added the tagged union Click.Info containing all necessary click info (e.g. slots)
• Made all inventories implement Viewable
• Simplified click handling and implemented vanilla parity other than special slots (like result slots) in ClickProcessors
• Moved click packet parsing & drag handling to each player's Click.Preprocessor
• Added Click.Result which stores a map of all changes and side effects that could occur
• Refactored InventoryCondition into InventoryClickEvent, and renamed what was formerly InventoryClickEvent into InventoryPostClickEvent
• More comprehensive tests
• Use ReentrantLock instead of Java synchronization
• Made cursor items PlayerInventory-based
• Greatly simplified inventory transaction logic
• Creative click logic and drop/swap logic in PlayerDiggingHandler is handled correctly (also removed PlayerSwapItemEvent)