Integrate Bower

I integrated Bower to easily manage dependencies.

`bower.json` lives in the root of the project, in order to be more intuitive. See https://github.com/driftyco/ionic-angular-cordova-seed/issues/10#issuecomment-33110624. Notice I didn't edit any project details here. Please update name, version, license, etc.

There is a `.bowerrc` file that modifies the installation destination into `www/bower_components`. I decided to name it `bower_components` instead of `components` as that is the default destination and is what most users are used to.

The only depedency so far is *ionic* as that package already includes `angular` and related.

Maybe you should update the `README` or tutorial to indicate that `bower install` has to be run after cloning.