DM-419

Forgot I could now create GitHub PRs for reviews.  Here it is; hope it's helpful.
If this was just about the transition period before meas_base can do everything the old meas_algorithms could do, I'd be more inclined to agree.  But this is also necessary to allow outputs produced by older versions of the pipeline to be read by newer versions of the pipeline.  Eventually I hope we can remove the backwards compatibility layer for that too, but I imagine that could be a long time after we've made the transition, and there's no longer any old outputs we care about being able to read.