kie-server: client now supports BASIC auth. method

This is just initial implementation to open the discussion about the client authentication.

I never really implemented anything like this, so there might be things I am missing. Every comment is more than welcome.

I did just manual tests. In future, ideally, all the integration tests could run against secured server (using the client).

@mrietveld could please take a look and share your experience with authentication in kie-remote?