Bug 22987: Add biblioimages.timestamp

Bug 22987: Add biblioimages.timestamp

This patch adds the timestamp column to the biblioimages table.
To test:
1. Apply this patch
2. Run:
   $ updatedatabase
   $ koha-mysql kohadev
   > SHOW CREATE TABLE biblioimages;
=> SUCCESS: Notice the new column is there with the right settings
3. Sign off :-D

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