Add support/document apps that use Vaadin for main UI as well

[mstahv]

url mapping etc is bit problematic currently, needs manual setup...

[mstahv]

Quickly tested, this works on top of start.vaadin.com project. Needs to be cleaned and preferably configurable route prefix.

As a depdencency:

    <dependency>
        <groupId>in.virit.entityexplorer</groupId>
        <artifactId>entity-explorer-base</artifactId>
        <version>0.0.1</version>
    </dependency>

Spring Boot configuration (e.g. to @SpringBootApplication class):

@EventListener
void registerRoutes(ServiceInitEvent evt) {
    RouteConfiguration configuration = RouteConfiguration
            .forApplicationScope();
    configuration.setRoute("entityexplorerabout", About.class, TopLayout.class);
    Arrays.asList(EntityEditorView.class, EntityExplorer.class)
            .forEach(view -> {
                configuration.setAnnotatedRoute(view);
            });

    // Better error handling, e.g. with Grid & error in lazy loading from backend
    evt.getSource().addSessionInitListener(e -> {
        e.getSession().setErrorHandler((ErrorHandler) event -> {
            UI current = UI.getCurrent();
            if (current != null) {
                current.access(() -> Notification.show("Error: " + event.getThrowable().getMessage()));
            } else {
                event.getThrowable().printStackTrace();
            }
        });
    });
}

[mstahv]

Preliminary instructions added in 29f603e

Keeping this open as a reminder to clean up/simplify.

[mstahv]

Fixed some NPEs in 0.0.2 in case a custom parent layout was used (e.g. views registered to apps main layout, not sure if that is a "best practice" by any means though). Example:

https://github.com/mstahv/sakila-spring-data-jpa-starter/tree/postgres-with-vaadin-ui-stub

[mstahv]

Now there is *-vaadin module that makes this easer. Still need to update that example branch in sakila project.