Error when editing date/time in assessment event notification

[elenaustyugova]

The bug is repeated when creating a notification and when editing an existing notification in the assessment event.

Steps to reproduce:

1. Go to the event details in the status "In progress" or "Not started"
2. Click on the create notification button/edit notification button
3. Close the pop-up
4. Click on the create notification button/edit notification button once again (reopen the pop-up)
5. Click on the date/time input (datepicker opens)
6. Close the date/time input

Actual result:

1. 2 errors appear: "Field is required", "Date cannot be in the past"
2. Datepicker icon is inactive

Expected result:

1. No errors appear
2. Datepicker icon is active

Req ID: REQF_adm_asss-011, REQF_adm_asss-012

[iperevozchikov]

@elenaustyugova Am I correnctly understand, that we should have ability to set notification at any date and ignore current validation about "date is in past"?