Add an additional option for group mechanics

[george112n]

Sometimes the idea of allowing all groups within a task to be simultaneously registered is not ideal, yet we still want there to be freedom in which group is started first. As an example, where a player has to select a side of a building and draw a line, and do this for all 4 sides, we don't really want them to do all of the selections first and then do all of the //line commands which currently is a perfectly valid way of completing such a step.

We could add an option such that once a group in a step is started (i.e once the first task in that group is completed), that group must be finished before any other groups are registered.
- Essentially all other groups would be unregistered and then reregistered once the that group has finished.

When starting a step the first task of each group would still all be registered, but once the first task of a group is completed the other groups will then be unregistered until all tasks in that group are completed. Once that group is completed, the first task of all of the other groups will have their listeners registered again and the process begins again.

Such a system would probably have to be specified on a step level, so all of the groups in a specific step would have to share the way in which they are registered and are completable.