Check the cardinality of the outcome variables, add more log
informations to nail the problem if it happens again

If the informations (size of file, max size allowed) is available,
validate first the size client side before making a validation on the
server.

lifecycle.

Differentiate managed and user created event in the personal calendar,
reactivate the icons for this in themes after upgrade of fullcalendar
library, better placement of the help in the calendars configuration

For the add operation, the start and end date is passed as ISO 8601
dates to prevent issues with timezone and daylight savings