apply_cal shadows hera_cal's apply_cal

[steven-murray]

THis is not necessarily a problem with aipy per se, but should be figured out. I just had a head-scratcher where I was running apply_cal.py via makeflow and it was telling me that a particular option wasn't available. I realized that the apply_cal.py in my env had been over-written by aipy's version.

We could

1. Do nothing, just let the user figure it out and re-install hera_cal after any aipy update.
2. Remove or rename the script in aipy (or hera_cal I guess)
3. Shift aipy (and/or hera_cal) to a subcommand style script system, so eg. $ aipy apply-cal [infile] [outfile] instead of $ apply_cal.py [infile] [outfile]