re-implement Scheduler as an interface and implementing instance
make it possible to implement external player collections
refactor and move to utils package
refactor PlayerHelper to PlayerUtils and move to utils package
refactor ItemStackHelper to ItemStackUtils and move to utils package
refactor mode to policy
refactor InventoryHelper to InventoryUtils and move to utils package
move GiveKitEvent to events.kits package
refactor EconomyHelper to EconomyUtils and move to utils package
fix incorrect scheduler package
minor code cleanup
minor code cleanup