Added Constants class and removed mapping of workflow input names
- Added Constants class with general constants.
- Renamed and moved the constants TEST_WORKFLOW_NAME_1, TEST_WORKFLOW_NAME_2, and TEST_WORKFLOW_NAME from WorkflowRunnerVersion2 to Constants.
- Removed mapping of workflow input names from GalaxyWorkflowEngine.prepareWorkflow.
- Used WorkflowInput1 and WorkflowInput2 for the Concatenate workflow (instead of input1 and input2).