LMS-597 Introducing ICallbackListener in AbstractAsyncCallback for testing purposes.

.../client/web/client/application/AbstractAsyncCallback.java

...openbis/generic/client/web/client/application/Client.java

.../client/web/client/application/DummyCallbackListener.java

...eric/client/web/client/application/ICallbackListener.java

...eric/client/web/client/application/ui/AddGroupDialog.java

...ric/client/web/client/application/ui/AddPersonDialog.java

...neric/client/web/client/application/ui/AddRoleDialog.java

.../generic/client/web/client/application/ui/GroupsView.java

...generic/client/web/client/application/ui/LoginWidget.java

...generic/client/web/client/application/ui/PersonsView.java

...s/generic/client/web/client/application/ui/RolesView.java

...bis/generic/client/web/client/application/ui/TopMenu.java