Fixed and improved docs

- Made docs consistent with Code
- Replaced commands to use cdap-cli
- Updated and tested all commands to work.

Build : https://builds.cask.co/browse/CG-SGUT1-1
Can we improve these names? I think "PageRankApp.PAGE_RANK_RANKS_SERVICE" is a bit of a mouthful. What about "PageRankApp.RANKS_SERVICE"?