Add amino acid substitution models

[richelbilderbeek]

Is your feature request related to a problem? Please describe.

Currently, there is only a nucleotide substitution model. This is unhelpful when working with proteomes.

Describe the solution you'd like

I would like to have the standard amino acid substition models implemented.

Describe alternatives you've considered

None.

Additional context

These are:

• Blosum62: Amino acid substitution matrices from protein blocks
• Dayhoff: 22 a model of evolutionary change in proteins
• JTT: The rapid generation of mutation data matrices from protein sequences
• CPREV: Plastid genome phylogeny and a model of amino acid substitution for proteins encoded by chloroplast DNA
• MTREV24: Model of amino acid substitution in proteins encoded by mitochondrial DNA
• WAG: A general empirical model of protein evolution derived from multiple protein families using a maximum-likelihood approach