Ionic serve and live reload need security (expose all code to anyone on same network).

Ionic serve and live reload need security, currently it exposes all code to anyone on same network. Its *very* helpful to be able to bind to external IP and open the URL on a bunch of ios and android devices and different browsers and have all of them refresh automatically with every code change. But this also opens it up to everyone else on the network.

It needs multiple sub-features, but the simplest and easiest to add should be this:
- Add basic http auth support. Developer will need to type in the a username/password only once when it run it for the first time. And it will allow them to allow access to others if they want to, change credentials in command-line parameters, etc... (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Authorization)

These can be optionally added later:
- Add https support, even if with just a self-signed certificate. Will secure against network sniffers, and as a side-effect also allow testing for https compatibility of actual app.
- Maybe add a url parameter `?token=aaaaaa` with a random token to allow both security and easy sharing. I have seen some tools do this, but personally I would prefer http basic auth + https.

Start by tracing the Ionic CLI's serve and live reload entry points, especially how they bind to an external IP and serve code to connected devices. Define how optional HTTP Basic Auth and command-line credential changes should work, then verify that unauthenticated network access is blocked while authorized browsers and devices can still reload. No file or test path is named in the issue.

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