Configurable download directory
- Workflow: added download directory getter and setter.
- BaseWorkflow: added download directory field (with getter and setter).
- GalaxyWorkflowEngine: used the download directory in the downloadOutputFiles method.
- GalaxyWorkflow: renamed inputs and outputs fields to inputsMetadata and outputsMetadata.
- GalaxyWorkflowTest: use renamed getInputsMetadata and getOutputsMetadata methods.