Add per-world spawn limits with fallback to server-wide bukkit.yml settings.

Fixes BUKKIT-1565

src/main/resources/configurations/bukkit.yml

@@ -23,6 +23,10 @@ settings:
     use-exact-login-location: false
     plugin-profiling: false
     connection-throttle: 4000
+spawn-limits:
+    monsters: 70
+    animals: 15
+    water-animals: 5
 ticks-per:
     animal-spawns: 400
     monster-spawns: 1