Prepare release 2.8.1

See merge request !994

Resolve "Allow overriding settings in trusted apps"

Closes #675

See merge request !993

Release 2.8

See merge request !992

Resolve "Change material icon set"

Closes #258

See merge request !686

Revert "Merge branch '665-account-adapter-overwritten-for-invitations' into 'master'"

See merge request !988

This reverts merge request !986

Resolve "Account adapter overwritten for invitations"

Closes #665

See merge request !986

Merge branch '663-password-reset-cannot-be-enabled-disabled-independently-of-password-change' into 'master'

Resolve "Password reset cannot be enabled/disabled independently of password change"

Closes #663

See merge request !985

Allow scheduling notifications by setting a send datetime

See merge request !983

# Conflicts:
#   CHANGELOG.rst
#   aleksis/core/models.py

[Docs] Add missing bracket in config example

See merge request !984

Implement StaticContentWidget

Closes #662

See merge request !981

[Docs] Fix references

See merge request !982

Resolve "Add configurable username validator for signup"

Closes #664

See merge request !980

Update dependency django-phonenumber-field to v6

See merge request !774

Update dependency django-reversion to v5

See merge request !977