Add ability to downgrade migrations by the absolute apply time
Add changelog line related to #2499
doc update about behavior.
Merge pull request #2499 from resurtm/migrate-to-datetime

Add an ability to downgrade migrations by the absolute apply time
Fixes #2487
Fixes #2460: custom listview/gridview summary was broken
Fixes #2458: Added missing validaton to advanced app forms, separated validation from email sending errors for contact form
Fixes #1578