[FIX] API: Collaboration fossil getStartDate

- If None, get from conference
[IMP] RegForm Angular speedup
[FIX] RegForm: No available events message

It now appears only in multiple selection
[FTR] Angular Dialog loads templates when opening
[FIX] RegForm: adapt dialogs to new ndDialog
[FIX] RegForm: Personal Data disable button
[MIN] Fail early if migration task has no docstring
[IMP] RegForm Angular speedup
[IMP] RegForm: SectionManagement dialog auto-close
[IMP] RegForm: Scroll to new section
[IMP] RegForm: Empty GeneralSection placeholder
[IMP] i-button danger: add hover and action effect
[IMP] RegForm: Highlight of new sections
[IMP] RegForm: Highlight recover section button
[FIX] RegForm: Phone field size