Refactor DataUtil and other cleanups

[magicus]

This PR contains the following cleanup/refactorings:

• DataUtil were reshaped into CurrentWorldPos. Methods which did not fit into this functionality where moved elsewhere.
• GameRulesUtil.needRenderCaves() were turned into allowCaves to align with other methods; the "need" functionality were moved to Layer.shouldRenderCaves()
• Rename methods to show that they are executed each tick.
• Other renames for clarity
• Make Layer an enum
• Reorder members in EntityHeadIconImage to conventional order
• Move functionality from MapPlayer to PlayerHeadIconImage where it is used
• Remove some dead code