Move plugin declarations to plugin syntax

Note: this syntax automatically applies the plugin to the root project.
Adding `apply false` in the plugin declaration disables that.

Issue: SPR-15885

settings.gradle

@@ -1,3 +1,14 @@
+/*
+pluginManagement {
+	repositories {
+		maven {
+			url "https://dl.bintray.com/kotlin/kotlin-eap-1.1"
+		}
+		gradlePluginPortal()
+	}
+}
+*/
+
 include "spring-aop"
 include "spring-aspects"
 include "spring-beans"