tracker-extract-gstreamer: Make date/time detection smarter

There's files that may have both GST_TAG_DATE_TIME and GST_TAG_DATE,
in some cases both will be "the same" and the former will be just
a more exact representation.

However for other cases (notably albums ripped in m4a), it is more
likely that the album release date is contained in GST_TAG_DATE,
while the other tag is more likely to contain the ripping time, or
something equally random.

For those cases where both dates are present but different, actually
prefer GST_TAG_DATE even though it's "less exact" in terms of
resolution. This also is more in line with how totem and rhythmbox
handle these fields.


Closes: #16
2 jobs for wip/carlosg/album-dates in 6 minutes and 14 seconds (queued for 2 seconds)
Status Job ID Name Coverage
passed #78823


passed #78824