Add posibility for a rollback if a step in the ChangeSet execute fails

[mnugter]

1. You should be able to get failed tasks from a ChangeSet.
2. Rollback must execute the opposite tasks of the original tasks.
3. Rollback must not trigger automatically but via a separate call
4. The documentation should expand on this feature and clearly note the risks involved:

• The rollback might fail as well, potentially causing more problems.
• Rollback is not guaranteed as it's not a database transaction but a remote (server) call

[mnugter]

This will likely be some form of the Saga pattern:

http://gotocon.com/chicago-2015/presentation/Applying%20the%20Saga%20Pattern
https://www.youtube.com/watch?v=xDuwrtwYHu8&t=305s