feat(art): add storybook meadow and woodland villagers

tools/import_storybook_grass.gd

@@ -0,0 +1,12 @@
+extends SceneTree
+## Run after Blender export and Godot import; the particle field requires a Mesh.
+
+
+func _initialize() -> void:
+	var scene := load("res://assets/storybook/meadow_grass.glb") as PackedScene
+	var instance := scene.instantiate()
+	var grass := instance.find_child("Grass", true, false) as MeshInstance3D
+	assert(grass != null)
+	var error := ResourceSaver.save(grass.mesh, "res://assets/storybook/meadow_grass.res")
+	instance.free()
+	quit(0 if error == OK else 1)