To indicate whether the state can be used as the follow-up state.
This is used by the state editor to filter out the follow-up drop down list. Currently, it is only used by the Application state, that is the first state automatically added, and cannot be deleted in any application.
As is now, it's not a very useful method. State should always implement it with a return of true.
Used by: state editor
True/false to indicate that it can be used as the follow-up state or not, respectively