Default: Convert saplings to use node timers

Each sapling is given a single node timer that is between
2 and 4 days of game play time (40-80 minutes). If you walk out
of the zone, and come back later, the tree will always grow
to full if the timer has elapsed.

Because trees.lua is all functions, it needs to be parsed before
nodes.lua, since that references some of its functions. Hence,
change the order of parsing here. Otherwise saplings would not
grow to full.