Simplify user configuration

[quentint]

Simplify user configuration by already pre-setting map and packages properties in System.config call argument.

User configuration is now easier, redundant calls like this are a thing of the past:

const map:any = {
  map: {
    'key': 'val'
  }
};

Here's how to use it now:

const map:any = {
  'key': 'val'
};

Same goes for packages.

ps: PRing this because it took me a while to figure out why my configuration wasn't working. This small improvement may help beginners!

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please let us know the company's name.

[quentint]

Just signed the CLA!

[googlebot]

CLAs look good, thanks!

[quentint]

Realizing I still have issues with SystemJS user configuration.

This PR may help, but it's still not enough for me, will dig into the docs a little more...

[quentint]

Forget it, this PR is dumb!

[angular-automatic-lock-bot]

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}