Draft: Add simple tests for generated scenes

It came up in !80 (merged) that we need to be vigilant about updating scenes when schemas change. Even though a lot of scene stuff is generated, most parts still rely on hard-ish-coded names of different schema attributes / nodes. So why don't we just programatically check that all the "keys" mentioned in widgets in generated scenes actually appear in device schemas?

It's not quite that easy and I don't currently have a DAQ schema in there, but will extend the proof of concept introduced in the first commit here (pointing against move-utils-out as the tests folder is moved to a nicer location then).