Automated Background; User Input Error Checks

- All user input requests are enclosed in error-check loops now.
- The task "Background" is now completely automated. It works fairly
well although not as perfect as if you ran it manually.
- ds9 pops open during apall for the science images for the user's
convenience (if they want to look for the SN spectrum in the 2-D
background-subtracted, wavelength-calibrated image).