babel extractors are now registered via python entry points,
so there is no need to declare babel extractors in babel configs.
This change is important to make translation work in Django 2.2.
django-babel does not work with Django 2.2 and looks unmaintained
for over two years. The horizon team is thinking to switch the extractor
to enmerkar (a fork of django-babel) to make extraction of translation
string work again near future. It is important to drop the extractor
definition to make the transition smooth.
Currently strings in Django templates cannot be translated
because the current recommended file pattern "templates/**.html"
does not match Django templates in subdirectories.
This needs to be "**/templates/**.html".
To enable translate job correctly, deleted heat-dashboard/locale
directory and updated babel-django.cfg accordingly.
Also fixed tox.ini which included wrong commands for docs build.