Drop Application.Controller access to internal

Now that MainWindow is in the Application package, we don't need to
keep Controller public anymore.

src/client/application/application-client.vala

@@ -156,17 +156,6 @@ public class Application.Client : Gtk.Application {
 
     }
 
-    /**
-     * The global controller for this application instance.
-     *
-     * This will be non-null in the primary application instance, only
-     * after initial activation, or after startup if {@link
-     * is_background_service} is true.
-     */
-    public Controller? controller {
-        get; private set; default = null;
-    }
-
     /**
      * The global email subsystem controller for this app instance.
      */
@@ -215,6 +204,17 @@ public class Application.Client : Gtk.Application {
         }
     }
 
+    /**
+     * The global controller for this application instance.
+     *
+     * This will be non-null in the primary application instance, only
+     * after initial activation, or after startup if {@link
+     * is_background_service} is true.
+     */
+    internal Controller? controller {
+        get; private set; default = null;
+    }
+
     /**
      * Determines if this instance is running from the install directory.
      */

src/client/application/application-controller.vala

@@ -13,7 +13,7 @@
  * A single instance of this class is constructed by {@link
  * GearyAplication} when the primary application instance is started.
  */
-public class Application.Controller : Geary.BaseObject {
+internal class Application.Controller : Geary.BaseObject {
 
 
     private const string PROP_ATTEMPT_OPEN_ACCOUNT = "attempt-open-account";