Publish browser version to Bower

Prepare for release of the browser build through [Bower](https://github.com/bower/bower). This will allow an easy `bower install cssom`.

The commit
- adds bower.json
- adds built CSSOM.js to repo under `dist/` and adjusts the Jakefile

When this is merged, a final step is needed once to publish the package to Bower (see https://github.com/bower/bower#registering-packages):

    $ bower register cssom git://github.com/NV/CSSOM.git

In the future however to update the published artifact it needs to be rebuilt and checked into the repo.