Rewrite furnace
* Move furnace related code into furnace.lua
* Move duplicated code into functions
* Rewrite ABM:
	* Easier to follow strcuture (no returns in the middle)
	* No unnecessary calls to get_craft_result
	* Split logic and "visual feedback" (a bit)
	* Fewer calls to meta:set and meta:get
	* Better feedback on the current state of the furnace
Correct node definitons for pine saplings and pine needles
Pinetree (by sfan5, from mg mapgen) lua generation and sapling ABM. Add checks for ignore to other trees