Update to Kotlin 1.60 and Gradle 4.9

Removes the dependency on legacy script compilation and now relies on script
discovery.  In addition, the Gradle build scripts were refactored and updated
to be compatible with Gradle 5.0 and make use of the new java-library
configurations.

game/src/main/java/org/apollo/game/model/entity/attr/AttributeMap.java

@@ -3,7 +3,6 @@ package org.apollo.game.model.entity.attr;
 import java.util.HashMap;
 import java.util.Map;
 
-import org.jruby.RubySymbol;
 
 import com.google.common.base.Preconditions;
 
@@ -118,8 +117,6 @@ public final class AttributeMap {
 				return new NumericalAttribute((Double) value);
 			case STRING:
 				return new StringAttribute((String) value);
-			case SYMBOL:
-				return new StringAttribute(((RubySymbol) value).asJavaString(), true);
 			case BOOLEAN:
 				return new BooleanAttribute((Boolean) value);
 		}

game/src/main/kotlin/org/apollo/game/plugin/kotlin/KotlinPluginScript.kt

@@ -13,11 +13,11 @@ import org.apollo.game.model.event.PlayerEvent
 import org.apollo.game.plugin.PluginContext
 import org.apollo.net.message.Message
 import kotlin.reflect.KClass
-import kotlin.script.templates.ScriptTemplateDefinition
+import kotlin.script.experimental.annotations.KotlinScript
+import kotlin.script.experimental.annotations.KotlinScriptFileExtension
 
-@ScriptTemplateDefinition(
-    scriptFilePattern = ".*\\.plugin\\.kts"
-)
+@KotlinScript("Apollo Plugin Script")
+@KotlinScriptFileExtension("plugin.kts")
 abstract class KotlinPluginScript(private var world: World, val context: PluginContext) {
     var startListener: (World) -> Unit = { _ -> }
     var stopListener: (World) -> Unit = { _ -> }