DATAREST-293: Add a separate module that contains the HAL browser

This adds spring-data-rest-browser as another module. That way, people aren't forced to add it to their app, but they can easily by just adding another dependency.

There are no test cases because this is simply inserting a static web application along with license material found at https://github.com/mikekelly/hal-browser.

I verified manually that this works with spring-a-gram by firing up my sample application and navigating to localhost:8080/browser/index.html