Bug 13622: Display a datetime without time in a notice

Bug 13622: Display a datetime without time in a notice

For some needs, a librarian would like to display a datetime or
timestamp field without the time.

This patch adds filter logic in the notice/letter parsing process.

Test plan:
1/ Defined a notice using a datetime or timestamp DB field
(biblio.timestamp for instance).
2/ Generate the notice
3/ Verify that the letter is generated with the time
4/ Use the "dateonly" filter like:
  <<your_table.your_field | dateonly>>
  <<biblio.timestamp | dateonly>>
5/ Generate the notice
6/ Confirm the the letter is generated without the time for this field.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Indranil Das Gupta (L2C2 Technologies) <indradg@gmail.com>
Updated the count of tests to 64 for t/db_dependent/Letters.t to pass
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>