Fix 'clean_affiliation' function
Fix 'clean_affiliation' function

- Define 'sunet_id' and 'stanford_department' error messages
- Modify cleaning function to check for both existance and validity of fields

Stanford-Online/edx-platform,Stanford-Online/edx-platform,caesar2164/edx-platform,caesar2164/edx-platform,caesar2164/edx-platform,Stanford-Online/edx-platform,caesar2164/edx-platform,Stanford-Online/edx-platform