models: use unittest2 style assertIsInstance test

Signed-off-by: Kai Blin <kai.blin@biotech.uni-tuebingen.de>
utils: Focus on counting codons correctly

Signed-off-by: Kai Blin <kai.blin@biotech.uni-tuebingen.de>
print codon table. Actually do something useful

Signed-off-by: Kai Blin <kai.blin@biotech.uni-tuebingen.de>