Add the option to allow calling vassals into wars mid-game.

[Trashcycling 17]

The only way I found to do this is to manually overwrite false to true in the details.json file, which is not something that the more "casual" people want to do. Just add some sort of console command and/or switch to toggle it.

[Question 22]

Yes, that would be nice. To be added as an option. Or to be honest. Makes sense to be the default. Since, the player has directlly the opportunity to choose if he wants to.