Change the package base name of the Go code, from
`git.blender.org/flamenco` to `projects.blender.org/studio/flamenco`.
The old location, `git.blender.org`, has no longer been use since the
[migration to Gitea][1]. The new package names now reflect the actual
location where Flamenco is hosted.
[1]: https://code.blender.org/2023/02/new-blender-development-infrastructure/
Move the UPnP/SSDP Manager autodiscovery code into from `main.go` into the
`worker` package. This also means changing the error handling a bit, as
only the `main.go` file is allowed to do `log.Fatal()`.
