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Major revision to the job-operation submission function.
- The write_user() function has been replaced by submit_user() with slightly adjusted API.
- The header and environment module have been merged into a single environment module.
- All submit logic has been removed from the scheduler drivers.
- Any submit logic implemented as part of the environment module has been reduced to the bare minimum.
- The submission flow has been refactored to be based on JobOperations.
- An attempt is made to detect the use of the deprecated API which will trigger the use of a legacy code path and the emission of warnings.
- Improved testing capabilities for unknown environments.
- The determination of present environments is deterministic and based on reversed definition order.
- Add the label decorators, allowing a more concise definition of methods which are to be used for classification.
- Add the FlowGraph, which allows the user to implement workflows in form of a graph.
- Implement unit tests for all core functionalities.