unicsv has inconsistent handling of date+time, date only, and time only fields

[tsteven4]

We have numerous inconsistencies related to partial date & time information in unicsv.
Perhaps we should store a date only as an invalid QDateTime with a valid QDate, and invalid QTime, and an indeterminate Qt::TimeSpec.
Perhaps we should store a time only as an invalid QDateTime with a invalid QDate, a valid Qtime, and an indetrminate Qt::TimeSpec.

unicsv interprets a date only as relative to UTC start of day and displays it translated to local time.
unicsv interprets a date and time as relative to local time.
unicsv regards zero time without date as invalid.
unicsv echos a non zero time without date as relative to the unix epoch and displays it translated to local time.

a date alone is interpreted as UTC start of day.
a date and time is interpreted as local
a time alone is interpreted as relative to the unix epoch

$ cat datetime.txt
name, lat, lon, date, time
dateonly, 36, -87, 2008-08-12,
dateandtime, 36, -87, 2008-08-12, 00:00:00
timeonly,36, -87, , 00:00:00
timeonly,36, -87, , 00:00:01
dateonly, 36, -87, 2008-12-12,
dateandtime, 36, -87, 2008-12-12, 00:00:00
timeonly,36, -87, , 00:00:00
timeonly,36, -87, , 00:00:01
$ cat xx
#!/bin/bash
cat datetime.txt;
TZ=/usr/share/zoneinfo/America/Denver ../../codeanalysis/bld/gpsbabel  -i unicsv -f datetime.txt -x transform,wpt=trk,del -o unicsv -F -
TZ=/usr/share/zoneinfo/America/Denver ../../codeanalysis/bld/gpsbabel  -i unicsv -f datetime.txt -x transform,wpt=trk,del -o gpx -F - | grep '\<time\>' | tail -6
TZ=/usr/share/zoneinfo/America/New_York ../../codeanalysis/bld/gpsbabel  -i unicsv -f datetime.txt -x transform,wpt=trk,del -o unicsv -F -
TZ=/usr/share/zoneinfo/America/New_York ../../codeanalysis/bld/gpsbabel  -i unicsv -f datetime.txt -x transform,wpt=trk,del -o gpx -F - | grep '\<time\>' | tail -6
$ ./xx
name, lat, lon, date, time
dateonly, 36, -87, 2008-08-12,
dateandtime, 36, -87, 2008-08-12, 00:00:00
timeonly,36, -87, , 00:00:00
timeonly,36, -87, , 00:00:01
dateonly, 36, -87, 2008-12-12,
dateandtime, 36, -87, 2008-12-12, 00:00:00
timeonly,36, -87, , 00:00:00
timeonly,36, -87, , 00:00:01
No,Latitude,Longitude,Name,Date,Time
1,36.000000,-87.000000,"dateonly",2008/08/11,18:00:00
2,36.000000,-87.000000,"dateandtime",2008/08/12,00:00:00
3,36.000000,-87.000000,"timeonly",,
4,36.000000,-87.000000,"timeonly",,17:00:01
5,36.000000,-87.000000,"dateonly",2008/12/11,17:00:00
6,36.000000,-87.000000,"dateandtime",2008/12/12,00:00:00
7,36.000000,-87.000000,"timeonly",,
8,36.000000,-87.000000,"timeonly",,17:00:01
    <time>2008-08-12T00:00:00Z</time>
    <time>2008-08-12T06:00:00Z</time>
    <time>1970-01-01T00:00:01Z</time>
    <time>2008-12-12T00:00:00Z</time>
    <time>2008-12-12T07:00:00Z</time>
    <time>1970-01-01T00:00:01Z</time>
No,Latitude,Longitude,Name,Date,Time
1,36.000000,-87.000000,"dateonly",2008/08/11,20:00:00
2,36.000000,-87.000000,"dateandtime",2008/08/12,00:00:00
3,36.000000,-87.000000,"timeonly",,
4,36.000000,-87.000000,"timeonly",,19:00:01
5,36.000000,-87.000000,"dateonly",2008/12/11,19:00:00
6,36.000000,-87.000000,"dateandtime",2008/12/12,00:00:00
7,36.000000,-87.000000,"timeonly",,
8,36.000000,-87.000000,"timeonly",,19:00:01
    <time>2008-08-12T00:00:00Z</time>
    <time>2008-08-12T04:00:00Z</time>
    <time>1970-01-01T00:00:01Z</time>
    <time>2008-12-12T00:00:00Z</time>
    <time>2008-12-12T05:00:00Z</time>
    <time>1970-01-01T00:00:01Z</time>