Reorganize repo

- Revamped gruntfile with `compile` and `dist` tasks replaced with `build` and `ship`.
- Everything moved into `src` directory.
- `grunt-usemin` is used in `_layouts/base.html` to reference minified versions of assets for production.
- There are now separate `watch:js` and `watch:css` tasks.

@ascott1  `npm install` and `grunt` and let me know if you run into any problems. Moving forward, `sheer serve` needs to be run from the `dist` dir instead of the project's root.

@fna This changes the app's deployment process which we can discuss after it gets merged.