[Draft] de-couple individual services

[PixelJonas]

This PR is stil a DRAFT - do not merge

As discussed in #647 - this is the start of making all hostnames / paths / ports configurable and being ultimately able to serve all individual components under their own domain-names.

Normal scenario should still be, that people are running all services one host, but having central service/place to get the locations of the other components enables us to support more deployment scenarios.

TODO

• [ ] There are still some SVELTE files in web using a relative path starting with /api
• [ ] websocket connections are still using a relative path
• [ ] upload ist still using a relative path