Merge lib/yard-cam.js into lib/image-record.js; they never should have been separate. (Oops.)

Much cleanup & reorganization & general foolery. (You'd think that an itty-bitty codebase like this one wouldn't *need* so much cleanup. But getting it right the first time is for people who already know what they're doing.)

Sorta-kinda implementation of /api/images/<id>. Needs work (e.g., error handling).