Console: Make NavHelper non-static

add NavService interface
hang off ClientAppManager
i2psnark: register additional instances with NavService

core/java/src/net/i2p/app/NavService.java

@@ -0,0 +1,29 @@
+package net.i2p.app;
+
+/**
+ *  Service to put links on the console.
+ *  Here so webapps can use it without dependency on console.
+ *
+ *  @since 0.9.56 adapted from console NavHelper
+ */
+public interface NavService {
+    
+    /**
+     * To register a new client application so that it shows up on the router
+     * console's nav bar, it should be registered with this singleton. 
+     *
+     * @param appName standard name for the app (plugin)
+     * @param displayName translated name the app will be called in the link
+     *             warning, this is the display name aka ConsoleLinkName, not the plugin name
+     * @param path full path pointing to the application's root 
+     *             (e.g. /i2ptunnel/index.jsp), non-null
+     * @param tooltip HTML escaped text or null
+     * @param iconpath path-only URL starting with /, HTML escaped, or null
+     */
+    public void registerApp(String appName, String displayName, String path, String tooltip, String iconpath);
+
+    /**
+     * @param name standard name for the app
+     */
+    public void unregisterApp(String name);
+}