increase selection box to show crop has matured, fix strawberry plant issue, add step to rhubarb growth

crops/wheat.lua

@@ -216,6 +216,7 @@ minetest.register_node("farming:wheat_7", table.copy(def))
 -- stage 8 (final)
 def.tiles = {"farming_wheat_8.png"}
 def.groups.growing = nil
+def.selection_box = farming.select_final
 def.drop = {
 	items = {
 		{items = {"farming:wheat"}, rarity = 1},