Support FreeRate model for site rate heterogeneity (Experimental).
Added -mset option to restrict model selection to models supported by RAxML (-mset raxml), MrBayes (-mset mrbayes), or Phyml/PartitionFinder (-mset phyml, -mset partitionfinder).
Fix bug concerning removal of identical sequences.
Fix bug concerning +I model (+G and +I+G were not affected).