CLI considerations for the case when users can disable identity mapping

[Nour-Mws]

These considerations were originally part of #298. Now that we've decided to defer the discussion on whether normal users need to be able to disable the identity mapping as a separate option, these are to be considered when that becomes relevant.

• Add the identity_mapping field to settings
• If identity mapping is on, log a message telling the user to turn it off for more accurate results
• Add a different exit code for the case where there are unresolved dependencies
• Add an unresolved deps section to the human output
• Change the output message for undeclared deps to make it clear that those are import names (not deps names)