Merging recent updates to dev branch

[charliekilpatrick]

Merging changes to:

• Fix dark ingestion and MOSFIRE frame characterization to properly import darks
• Moving threshold for generating final photometry catalog so more flux standards are incorporated down to S/N=20
• Remove caching for Vizier catalogs in case previous astroquery calls failed
• Stricter cosmic ray flagging with dynamic FWHM to better flag cosmic rays in well sample detectors
• Reverting to internal memory usage in ccdproc combine method to avoid errors and removing individual image weights