Bug 24840: Replace DateTime->now with dt_from_string

Bug 24840: Replace DateTime->now with dt_from_string

We should use Koha::DateUtils instead of Date::Time directly

This patch simplay replaces calls to now() with a call to dt_from_string()
which does effectively the same thing.

Probably reading the code and verifying changes is sufficient but...

To test:
1 - confirm the files all compile
2 - confirm all tests pass
3 - confirm Koha still works

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>