Feature Proposal: new TransitionAnchor widget in errai-navigation

#### Description
Created a new injectable widget called TransitionAnchor.  This widget extends GWT's Anchor and includes the navigation boilerplate, allowing simple links to be made from Page to Page within errai-navigation.

Example:

```java
@Templated("site/dashboard.html#page")
@Page(path="dashboard", startingPage=true)
@Dependent
public class DashboardPage extends Composite {
	@Inject	@DataField("aboutLink")
	private TransitionAnchor<AboutPage> aboutLink;
}
```

The above will inject an Anchor widget that, when clicked, will navigate to AboutPage.

#### What's Missing
Currently the "href" attribute of the Anchor widget is being properly set to the target page's history token.  However, errai-ui's Templating system will whack the 'href' attribute and replace it with whatever is in the template.  I'll bring this up in the forum or IRC to discuss possible solutions.