disable selecting multiple facial expressions

[alisaad673]

The face that multiple selection of facial expressions result in is quite bad. We either need to disable selecting more than one facial expressions, or we need some other solution

https://user-images.githubusercontent.com/35926530/181919766-7db0071b-0e78-4f23-aaef-a7fa6fac1628.mp4

[jakezira]

It seems quite bad while several facial expression is on, but users might still want complex facial expression than only single one. Maybe we can limit the value of total facial expression weight value, instead of disabling multiple facial expressions.