Parsing SingleFile datetime using dates.strpdate.
Adding timezone when no timezone info is available.
Installing python-dateutil to assist in handling diverse datetime strings.
Reworking refresh progress to use idempotency to display more accurate progress. Only logging that files have been invalidated if they used to be indexed.
Clearing archives to force re-index.
Ignoring 'Unknown' author from PDF metadata. Using file_title when pdf metadata title is empty.
