Make sure world names are lowercase'd

bukkit/src/main/java/me/lucko/luckperms/bukkit/WorldCalculator.java

@@ -45,7 +45,7 @@ public class WorldCalculator implements ContextCalculator<Player> {
         world = plugin.getConfiguration().get(ConfigKeys.WORLD_REWRITES).getOrDefault(world, world);
 
         if (world != null) {
-            accumulator.add(Maps.immutableEntry(WORLD_KEY, world));
+            accumulator.add(Maps.immutableEntry(WORLD_KEY, world.toLowerCase()));
         }
 
         return accumulator;

bungee/src/main/java/me/lucko/luckperms/bungee/BackendServerCalculator.java

@@ -41,7 +41,7 @@ public class BackendServerCalculator implements ContextCalculator<ProxiedPlayer>
         String server = getServer(subject);
 
         if (server != null) {
-            accumulator.add(Maps.immutableEntry(WORLD_KEY, server));
+            accumulator.add(Maps.immutableEntry(WORLD_KEY, server.toLowerCase()));
         }
 
         return accumulator;

common/src/main/java/me/lucko/luckperms/common/contexts/ContextManager.java

@@ -54,7 +54,8 @@ public class ContextManager<T> {
     }
 
     public void registerCalculator(ContextCalculator<T> calculator) {
-        calculators.add(calculator);
+        // calculators registered first should have priority (and be checked last.)
+        calculators.add(0, calculator);
     }
 
     public int getCalculatorsSize() {

sponge/src/main/java/me/lucko/luckperms/sponge/contexts/WorldCalculator.java

@@ -43,7 +43,7 @@ public class WorldCalculator implements ContextCalculator<Subject> {
         }
 
         Player p = ((Player) source);
-        accumulator.add(Context.WORLD_KEY, p.getWorld().getName());
+        accumulator.add(Context.WORLD_KEY, p.getWorld().getName().toLowerCase());
         return accumulator;
     }