added an extension point to modularize the system configuration page.

core/src/main/java/jenkins/model/GlobalConfiguration.java

+package jenkins.model;
+
+import hudson.ExtensionList;
+import hudson.ExtensionPoint;
+import hudson.model.Describable;
+import hudson.model.Descriptor;
+
+/**
+ * Convenient base class for extensions that contributes to the system configuration page but nothing else.
+ *
+ * <p>
+ * All {@link Descriptor}s are capable of contributing fragment to the system config page, so
+ * this extension point is is really only for those who don't want to contribute anything else.
+ *
+ * @author Kohsuke Kawaguchi
+ * @since 1.425
+ */
+public abstract class GlobalConfiguration extends Descriptor<GlobalConfiguration> implements ExtensionPoint, Describable<GlobalConfiguration>  {
+    protected GlobalConfiguration() {
+        super(self());
+    }
+
+    public final Descriptor<GlobalConfiguration> getDescriptor() {
+        return this;
+    }
+
+    /**
+     * Unless this object has additional web presence, display name is not used at all.
+     * So default to "".
+     */
+    public String getDisplayName() {
+        return "";
+    }
+
+    @Override
+    public String getGlobalConfigPage() {
+        return getConfigPage();
+    }
+
+    /**
+     * Returns all the registered {@link GlobalConfiguration} descriptors.
+     */
+    public static ExtensionList<GlobalConfiguration> all() {
+        return Jenkins.getInstance().getDescriptorList(GlobalConfiguration.class);
+    }
+}