added basic/digest backend example

in order to encapsulate the backends that we use in our cookbook demos  in a single repo, we opted to extract the [```http basic/digest```](https://github.com/aerogear/aerogear-integration-tests-server/blob/master/src/main/java/org/jboss/aerogear/integration/service/GroceryService.java) example from our [integrations-tests-server](https://github.com/aerogear/aerogear-integration-tests-server) and bring it to this repo. This should be easier for us to pinpoint to users both the native example and the backend that supports it (as we currently do)

During the extraction and cause of the deprecation of ```aerogear-security```,  it was a good chance to update the demo to use native picketlink only (used the latest rel version). Needed some changes, mostly replace web.xml with its sec filters with a [Builder](https://github.com/cvasilak/aerogear-backend-cookbook/blob/auth/Authentication/src/main/java/org/jboss/aerogear/integration/config/HttpSecurityConfiguration.java)

Tested on both wildfly-8.1 and eap-6.3 and works fine but I will appreciate @abstractj and @corinnekrych to have a look and update it if I miss something.