Merge branch 'feature/data-checks' into 'master'

aleksis/core/admin.py

aleksis/core/apps.py

aleksis/core/data_checks.py

aleksis/core/health_checks.py

aleksis/core/menus.py

aleksis/core/migrations/0008_data_check_result.py

aleksis/core/models.py

aleksis/core/preferences.py

aleksis/core/rules.py

aleksis/core/static/style.scss

aleksis/core/templates/core/data_check/list.html

aleksis/core/templates/templated_email/data_checks.css

aleksis/core/templates/templated_email/data_checks.email

aleksis/core/urls.py

aleksis/core/util/core_helpers.py

aleksis/core/views.py