Refactor snippets

Hi @victornadot , this MR is complementary to the one for the repository e3-ioc-nblm-power (which is the IOC to control the lab bench setup we have on site).

I had to refactor the snippets a bit, and when I did I noted both a few mistakes in macro-naming, but also realized that it's better for us to just have iocsh/nblm_crate*.iocsh be generic instead of hardcoded per crate configuration.