Add the `BatcherThread` foundation class.
Import the (un-tested) `sendmail` Django mail backend.
Import the (un-tested) `mail*` functions, which handle parallel mail sending and HTML stuff.
Merge branch 'develop' into feature/django-mail
Merge branch 'develop' into feature/django-mail
Merge tag 'sparks-1.17.3' into develop

1.17.3
Merge branch 'develop' into feature/django-mail
fix init context.
HTML email and BS4 fixes & enhancements.
fix on the fixture name (must not use '.' else Django fails miserably).
Noticeable enhancement in HTML mail images handling.
Merge branch 'develop' into feature/django-mail
Merge branch 'feature/django-mail' into develop
bump version in setup.py
Merge branch 'release/1.18'