Fix biomes leaves and saplings

[EmptyStar]

Major overhaul of Biomes modpack nodes, trees, and recipes:

• Ensure that there exists a sapling for each type of leaves
• Make the names of leaves and saplings more thematic, consistent, and color-agnostic
• Tweak some tree schematics to make them centered when placing via minetest.place_schematic
• Add Frost Land door + trap door + fence + gate
• Add missing wood stairs declarations
• Change craft recipe for scarecrow to be more thematic
• Change sapling craft recipes to be more consistent
• Add missing craft recipe for Jack o' Lanterns

These changes will fix #55 and prevent many other errors/crashes that were possible with the nodes in these biomes.

[EmptyStar]

These changes are mostly good to go, but I want to do a little more testing and tweaking before merging it. I've already tested a number of leaves and saplings and they are overall much more polished and functional.