Add a "layer"/"Z-Index" to Portrait Join event

[Crystalwarrior]

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Ability to have fine-tuning over which character sprite goes over who would be nice. Rather than re-calling join events in a specific order, simply having a "layer" which changes order of events in the background would work nicely (similar to Z-Index of sprites).