Set default maximum viewing range to a bit more than default server send range to make fog work well

Don't set m_removed on dead players (dead players are indicated by hp == 0). Local
damage flash is shown whatever the cause was (even from Lua set_hp). PlayerCAO
damage flash matches duration of local damage flash. Fall damage is dealt much more consistently (this is done by disallowing jumping when speed.Y is very negative, up to now jumping could sometimes negate fall damage)

ItemStack is a struct, not a class
CollisionInfo is a struct, not a class
InventoryAction is abstract and it needs a virtual destructor