Ensure latest node version is installed

This adds a new Grunt task: `bitc:fixnode`. `bitc-configurator` now depends on the npm API. It first removes the `apt` version of npm, then using the npm API (which is locally installed and therefore not removed by `apt`) installs `npm` and `n` (a node version manager) globally. With `n`, the latest stable version of `node` is installed globally, and the `apt` version is removed.

This ensures that the latest versions of `npm` and `node` are available in the global path.

They are later updatable by running `n stable` while connected to the Internet. The `apt` versions are almost always outdated, hence the need for a newer version to be installed manually.

*This is untested*, and I don't know how `bitc setup` will be affected by the changing of the node binary while it is running.