PvPIndex Battle

Fixed

• Flight exploit before battle (#28): players who jumped while flying before a battle were launched above the arena, causing the battle to be rejected. Flight and velocity are now neutralised before teleport, and again when applying pre-battle state.
• Explosions destroying arena blocks (#29): crystal, TNT, and other explosions could break blocks in arena worlds even when allow_block_break was false in the game mode rules. Added EntityExplodeEvent and BlockExplodeEvent listeners that clear the block damage list when block breaking is disabled. Explosions still deal damage to players.