Make it possible to differentiate by node

[snaens]

Currently you can only differentiate by message.
So having, say multiple camera nodes running means you can't pinpoint which one failed.

[snaens]

Instead I added nodename_diagnostics, which lets you spit out a diagnostic depending on whether a node is visible or not.

I did also try out log_diagnostics that require a certain node name,
but it was always a hassle to configure, so I dropped it.
If you wanna re-add it, all you gotta do is add a check here and save the node_name to the ErrorMessage class