Add large cactus seedling

Alter 'large cactus' schematic to place another force-placed cactus node,
to replace the cactus seedling on growth.
Make schematic 5x7x5 to solve rotation, placement and protection check
issues.
Add a y-slice probability for height variation.

Growth time is tuned to not make this a faster way to obtain cactus nodes
compared to normal cactus farming.
Seedling texture by Extex101.

Use sapling/seedling description in protection intersection message in
'sapling_on_place' function.

mods/default/license.txt

@@ -50,6 +50,7 @@ Copyright (C) 2010-2018:
   TumeniNodes
   Mossmanikin
   random-geek
+  Extex101
 
 You are free to:
 Share — copy and redistribute the material in any medium or format.