feat(app) binding navigation form - source (#379)

* the applicationWorkingCopy is updated when an user performs a
modification on the navigation
* newOprhanPage doesn't have default page name
* topMenu page is null instead of empty

closes[BS-16420](https://bonitasoft.atlassian.net/browse/BS-16420)

bundles/plugins/org.bonitasoft.studio.ui/src/org/bonitasoft/studio/ui/viewer/LabelProviderBuilder.java

@@ -150,7 +150,7 @@ public class LabelProviderBuilder<T> {
             public String getText(Object element) {
                 try {
                     final T e = (T) element;
-                    return textFunction.map(function -> function.apply(e)).orElse(super.getText(element));
+                    return textFunction.map(function -> function.apply(e)).orElse("");
                 } catch (final ClassCastException e) {
                     return super.getText(element);
                 }
@@ -205,7 +205,7 @@ public class LabelProviderBuilder<T> {
             public String getText(Object element) {
                 try {
                     final T e = (T) element;
-                    return textFunction.map(function -> function.apply(e)).orElse(super.getText(element));
+                    return textFunction.map(function -> function.apply(e)).orElse("");
                 } catch (final ClassCastException e) {
                     return super.getText(element);
                 }