Retry transaction if there are conflicts, Closes #28

config/api_example_config.py

src/api/announcement.py

src/api/authentication.py

src/api/course.py

src/api/database/__init__.py

src/api/database/abstract_py_connector.py

src/api/database/database.py

src/api/database/mysql_connector.py

src/api/database/postgres_connector.py

src/api/database/sqlite_connector.py

src/api/job.py

src/api/objects/current_changelog.py

src/api/objects/object.py

src/api/routes/courses.py

src/api/routes/object_modifications.py

src/api/routes/site.py

src/api/routes/sorter.py

src/api/routes/user.py

src/api/user.py