won't let you add a stage with the same name
disables you from adding a stage when a stage of that name exists
shows an error message if you try to add a stage that already exists
adds test to make sure a new stage isn't added when you try to make a duplicate
Merge branch 'dev-gradle' of github.com:slash-slash-no-comment-WPI-cs3733/wpi-suite into stage_ids

Conflicts:
	TaskManager/src/main/java/taskManager/model/WorkflowModel.java
throws an exception if the workflow fails to instantiate a stage
Merge branch 'dev-gradle' of github.com:slash-slash-no-comment-WPI-cs3733/wpi-suite into stage_ids
Merge branch 'dev-gradle' of github.com:slash-slash-no-comment-WPI-cs3733/wpi-suite into stage_ids