Merge branch 'mattias_feature_assignment'

bbcli/cli.py

bbcli/commands/assignments.py

bbcli/services/__init__.py

bbcli/services/announcements_service.py

bbcli/services/assignment_service.py

bbcli/services/contents_service.py

bbcli/services/courses_service.py

bbcli/services/utils/content_builder.py

bbcli/utils/URL_builder.py

bbcli/utils/error_handler.py