[ModelicaSystemDoE] simplify definition; use a Modelicasystem instance as argument

[ModelicaSystemDoE] update docstring

[ModelicaSystemDoE] fix for relative paths

[ModelicaSystemDoE] fix unittest

* test_ModelicaSystemDoE_local is tested
* test_ModelicaSystemDoE_docker should work
* test_ModelicaSystemDoE_WSL is untested

[ModelExecution*] create classes to handle model execution

* rename ModelicaSystemCmd => ModelExecutionCmd
* rename OMCSessionRunData => ModelExecutionData
* create class ModelExecutionException
* move some code:
  * OMCSession.omc_run_data_update() => merge into ModelExecutionCmd.define()
  * OMCSession.run_model_executable() => ModelExecutionData.run()

[test_ModelicaSystemCmd] update unittest

[ModelExecutionData] include the original exception if reraised as ModelExecutionException

[ModelicaSystem] fix usage of ModelicaSystemCmd

…existable exists and can be executed

[ModelicaSystem] split ModelicaSystem into ModelicaSystemABC and ModelicaSystem

[ModelicaSystem] rename ModelicaSystem => ModelicaSystemOMC

* add compatibility variable for ModelicaSystem

[test_ModelicaSystemOMC] rename from ModelicaSystem and update

[test_*] use ModelicaSystemOMC

[ModelicaSystem*] fix last usages of ModelicaSystem() in comments & docstrings

[ModelicaSystem] split ModelicaSystemDoE into ModelicaDoEABC and ModelicaDoE

[ModelicaSystem] rename ModelicaSystemDoE => ModelicaDoEOMC

* add compatibility variable for ModelicaSystemDoE

[test_ModelicaDoEOMC] rename from ModelicaSystemDoE and update

[ModelicaSystem] update ModelicaDoEABC to use ModelicaSystemABC

[ModelicaSystem] define doe_get_solutions() as separate method