Read NoMAD configuration values from Managed Preferences (#50)
Read NoMAD configuration values from /Library/Managed Preferences before
reading them from ~/Library/Preferences.
In manual testing with split preferences, UseKeychain is now being read
from Managed Preferences plist while UserPrincipal is still being read
from the user's preferences plist.
This will avoid users having to use that manual workaround on corporate
managed devices that deploy a configuration profile to manage NoMAD.
Fixes: #32
Co-authored-by: Seng Ern Gan <sengern.gan@anz.com>
