add mixture models for modelfinder2

[roblanf]

Here's a list of things we can add to the mixture models list

https://github.com/iqtree/iqtree3/blob/master/model/modelmixture.cpp

UDM 4 to UDM 4096

MEOW80 from Andrew Roger's group

Check Hector Banos' recent papers.

Feel free to add any other mixture models we should add in.