Create override imap folders if needed

[jyellick]

The delivery allows for user overrides to affect the destination imap folder. The function documentation indicates that if the destination folder does not exist, it will be created. However, the creation function only works for explicitly set folders, not for the overrides.

This change creates a simple GetOrCreate user call for an imap folder. It then leverages this call both in the original non-override path as well as the override path.