Plan stages

Journeys can now be grouped into stages for greater control over how they will run within the plan. Each stage can specify whether the journeys in that stage should run sequentially or in parallel. Subsequent stages will not begin execution until all previous stages have completed, so dependencies between journeys can be modeled by placing them in different stages. A stage can also be marked as always run which means that it should be executed even if a failure occurs in a previous stage, enabling patterns such as set up / test / tear down. See plan stages for more information.