Rename method to clarify use. #3997.

This method is only useful in importer contexts. Normal Cases
operation should use #advance.
Remove implicit switching to hi. #3997.

The next commit on this branch will start using participant consents
directly to determine the date of high-low conversion. This should be
accurate enough that implicit switching will be an error.
Determine hi entirely based on consents given. #3997.

This change eliminates the requirement that a participant consent be
associated with consent event in order to be able to trigger a lo-hi
conversion. The import process will now check if the participant
should be in hi at each event based on her consent history. She will
be transitioned to hi for the first event which ends on or after her
first hi consent.