Better logging when electron/self-hosted doesn't start up correctly.

[daed]

See Laverna/laverna#985 for background.

Docker competes for port 9000. Maybe we can display something informative if the webserver can't start because port is in use?

[Maks-s]

Or we can change the port, and if it's also used then check the next one.
As we don't want to check 56535 port, we can just check for number 9000 to 9000 + X

[daed]

That would work for desktop versions. If you run it as a server, I would think that you'd wouldn't want inconsistency there.

[pms1969]

VSCode does this very well if you're looking for an example.

[daed]

@Maks-s put in a check and error message for this via #74. I don't know if we should talk about changing ports to something less commonly used or if this is enough, but I think I'm satisfied with, at least for the time being.