Fixes XWALK 2704

- Restores `.gitignore` file
- Fixes template for v0.4.0 of the styleguide generator
- Moves the `styleguide.md` file into `public/` where it should have been
- Improves `npm run` scripts

Now, `npm run styleguide` will properly build the styleguide again, `harp compile` will continue to build the static version to `www/` and `npm run compile` is a shortcut to do both.