Dataset-creator

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* Fixed making dataset as aminoacid seqs for MEGA format.
* Fixed making dataset as degenerated seqs for MEGA format.
* Fixed making dataset as degenerated seqs for TNT format.
* Fixed making dataset as aa seqs with specified outgroup for TNT format.
* Raise ValueError when asked to degenerate seqs that will go to partitioning
based on codon positions.
* Dataset creator returns warnings if translated sequences have stop codons '*'.
* Cannot generate MEGA datasets with partitioning.

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* Fixed 2nd, 3rd codon positions bug that returned empty FASTA datasets.

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* Fixed 3rd codon positions bug that returned FASTA datasets with 3rd codon
positions even if they were not needed.

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* If user provides outgroup, then TNT datasets will place its sequences in first
position in the dataset blocks.

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* Fixed bug that did not show DATATYPE=PROTEIN in Nexus files when aminoacid
sequences were requested by user.

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* Fixed bug that raised an exception when SeqExpandedRecords did not have data
in the ``taxonomy`` field.