Bug 28408: Add 'Last updated' column to suggestions table

Bug 28408: Add 'Last updated' column to suggestions table

We have specific meanings for the different dates in suggestions
Managed - means the status was changed or the suggestion edited, but doesn't change if item type updated
Modification - implies an edit of the subscript, not updated if status changed alone
Updated - this is the date field in the DB, which is actually a timestamp

The cronjob purge_suggestions.pl uses teh 'date' field

For a user, a suggestion can look old in the interface, but be considered recent by the script

To clear the confusion we should show the timestamp as well

To test:
1 - Add a suggestion
2 - In the DB, pretend you set it in the past:
    UPDATE suggestions SET manageddate='2021-01-01', suggesteddate='2021-01-01', date='2021-01-01 12:12:12';
3 - Click 'Go' In Organize by: Status
4 - Note the suggestion looks old now
5 - Check the box, and click 'Update item types with:' -> Submit
6 - Prganize by status again
7 - No change?
8 - Check the DB:
    SELECT date FROM suggestions;
9 - The field is updated
10 - Apply patch
11 - Organize by status again
12 - See the 'Last updated' ate set to today

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>