Make objectForm implicitly handle undefined isCreate

See merge request !1798

Update changelog from 4.0.1

See merge request !1799

depending on the presence of editItem.

For the rationale see comment in change.

Fix dialog-Object-Form's internal dialog-mode-handling

See merge request !1793

Update dependency django-maintenance-mode to ^0.22.0

See merge request !1775

# Conflicts:
#   CHANGELOG.rst
#   aleksis/core/frontend/components/generic/dialogs/DialogObjectForm.vue

Saveguard calendarSelectedFeedsMixin calendar-query against no data

See merge request !1791

Make DialogObjectForm slightly wider

See merge request !1792

Update dependency html2text to v2025

See merge request !1794

and move to proper places.

Now the dialog-mode can be set from parent via v-model and from child
via #activator. The later was previously broken.

The new placement just makes more sense with the mixins.

At least on my laptop this allows to display two datetime-fields next
to each other. Which was previously not possible.

This threw an error on mount previously.

Update renovate.json

See merge request !1789

Resolve "Show announcements in calendar"

Closes #976

See merge request !1772

Resolve "OAuth: Activate upload of icons"

Closes #1215

See merge request !1784

# Conflicts:
#   CHANGELOG.rst

Resolve "Recurrences without rrule_until don't work"

Closes #1255

See merge request !1783

# Conflicts:
#   CHANGELOG.rst

Resolve "Frontend does not respect configured theme"

Closes #1258

See merge request !1781

Fix frontend components imports

Closes #1253

See merge request !1782

Resolve "PersonalEvents with fullDay error in backend"

Closes #1256

See merge request !1777