Automatic fetching of latest xbs-api and services + npm build error fix

[steccas]

Hi, I tought to send this PR because I noted the probles that I've reported with issues #21 and #22 .

The build is now smooth and clean and keeping the xbs api updated is now easier.

[nero120]

Thank you for this @steccas, looks great! I've very little free time at the moment but will review this soon.

[steccas]

Thanks @nero120, please bear in mind that the fact that the dockerfile grabs the latest xbs version has some implications.

So maybe we can consider some CI/CD that keeps the image on the HUB updated, like running a build on a new release of xbs or maybe just scheduling. (like I did in my repo with github actions)