Rewrite viewer using AngularJS

[ramnathv]

The idea is to create a leaner and more flexible implementation of the viewer. Desired features are:

1. Ability to display contents in a modular fashion:
   • README.md
   • code.R
   • index.html
2. Switch seamlessly to interactive mode.
3. Be able to fork easily.

This viewer is expected to share a lot of the features from the slidify playground. So it makes sense to develop both apps in tandem, maybe even factoring out common routines for reuse.

[ramnathv]

I can use http://bl.ocks.org/ to render the page. Alternately, I could write my own renderer code, which I believe should be reasonably straightforward.