Add support for NPM releases

Adds the `grunt-release` npm package to `dev-dependencies` and updates the options to only push to npm (instead of bumping version, creating tags, pushing tags)

This fix is for: https://github.com/angular-ui/angular-google-maps/issues/964

Test: 
```bash
# Does a dry run
grunt release --no-write
``` 

Verify that the dry run only pushes to npm without anything extra.
The options set around bump take care of bumping the version for both bower and npm (if you see that it is specifying package.json as one of the files that gets updated). And then the options for release limit it such that it only publishes to npm instead of also bumping the version, committing the package.json file, creating a new git tag, pushing to remote, pushing tags to remote and then pushing to npm.

Testing my code without any options for release ends like this:
![1___zsh_tmux_plugin_run__tmux_](https://cloud.githubusercontent.com/assets/1082191/5304463/1f6f6fea-7bb0-11e4-8f26-6c08d5889b70.png)

Testing my code with release options looks like this:
![1___zsh_tmux_plugin_run__tmux_](https://cloud.githubusercontent.com/assets/1082191/5304478/415d62a6-7bb0-11e4-922f-3ec7c2aeb326.png)

If I understood the implementation details correctly you wanted bump-@ to bump and then release. If this was not your desire I can add a separate target called release which runs the bump and then runs release. (though that will theoretically be 3 targets so that you have a release-@, release-@-major and a release-@-minor)