moved perlin seeddiff settings to respective mods' init.lua's, tweaked default

perlin values to be the same as used in the game's mapgen for spawning dry
shrubs and jungle grass, so that jungle grass mod will replenish the game's
biomes.

junglegrass/init.lua

@@ -4,6 +4,7 @@ local spawn_delay = 2000 -- 2000
 local spawn_chance = 100 -- 100
 local grow_delay = 1000 -- 1000
 local grow_chance = 10 -- 10
+local junglegrass_seed_diff = plantlife_seed_diff
 
 local grasses_list = {
         {"junglegrass:shortest","junglegrass:short" },