1. docstrings for define_visits and ingest_raws are missing so butler --help displays not-useful information for these commands

2. change butler register-instrument so that instrument is an arg instead of an opt butler register-instrument REPO lsst.obs.lsst.Latiss (without the -i). It should take multiple values for INSTR.

3. If obs_base is set up such that a commands yaml is found but obs_base is not importable, butler --help falls over in a big heap. I think we should protect the doImport in cmd = self.get_command(ctx, subcommand) and issue a “could not import sucommand X” warning but continue on.

4. in butler --help, sort the commands alphabetically