Update to reflect change from mvn to gradle

The only changed file in this fork is architecture/uaa.html.md. Nearly all of the edits are updates to the instructions for building and running the UAA and the sample programs. The build is now Gradle based.

However, in reviewing the material covered in this document, I noticed that all, or nearly all of the content of this document is already covered in the documents in the actual UAA repository. Rather than maintain the information in two different places and be subject to future changes like this one from Maven to Gradle, I think a better approach would be to just have the document in docs-cloudfoundry-concepts/architecture/uaa be a pointer to the relevant docs in https://cloudfoundry/uaa (the README.md and the files in the docs directory). <a href="mailto:fhanik@pivotal.io">Filip Hanik</a>, one of the key contributors to the UAA agrees. 

I wasn't quite sure how to express that desire in a pull 
cbenson@pivotal.io