Add support to find duplicates based on photos with same-size+same-photodate

[k3b]

gui:

Menu: Duplicates-Filter

show result in folder-picker with dates which is used by the date-(range)-filter with contextment show in new gallery

Finding duplicates via sql similar to this

select size, photoDate, min(id) as id, min(... group by size, photoDate having count(size) > 1