SAK-50733 Date Manager CSV export/import and Excel date compatibility

[st-manu]

https://sakaiproject.atlassian.net/browse/SAK-50733

The "SAK-50066: Date Manager: export / import csv feature for batch updates feature" enables the export/import of a CSV containing dates from the Date Manager. However, it is not possible to import a CSV edited with Excel, as Excel breaks the format. Additionally, several points need to be addressed:

• The "Draft" label is not exported, making it impossible to distinguish between draft and published items with the same name, except by ID.
• Gradebook only support dates, not times. However, the exported CSV includes date + time, leading users to believe that time can be defined.
• The Date Manager blocks fields that cannot be edited. It should indicate during export (and in the CSV headers) which fields are requiered, which can be modified, left blank, or assigned a value even if they were previously empty.
• Leaving a field blank sometimes causes subsequent fields to not be checked, and the blank value is ignored.
• Some fields, when left blank, are auto-filled with the current date and time.
• Titles with characters sensitive to CSV formatting cause errors during import.