Sort by date sorts only by year

When sorting by date it does not take the date into account, only the year. Especially with the banknotes we are adding specific dates, so it would be usefull to use the full date to sort.

For example the interesting year 1923 in Germany:

https://en.numista.com/catalogue/index.php?e=allemagne-pre1945&r=&ct=banknote&im1=&im2=&tbb=y&cat=y&ru=&ca=931&no=&v=&i=&b=&ie=&u=&a=1923&dg=&m=&f=&t=&t2=&mt=&g=&se=&d=&c=&wi=&sw=&o=y