Updating `summarize_distances` function.

Adding `full_aligner_tools` keyword argument to `summarize_distances`
function of the `seqstats` module. This allows the caller to specify a
separate prioritized list of alignment executables for pairwise and full
alignment.
Adding `--msa-aligner` CLI option to `seqvet.py`.

This option allows the user to specify a separate alignment program
executable to use for a full multiple sequence alignment.
Merge branch 'master' of phylo.bio.ku.edu:SeqSift

Conflicts:
	scripts/seqvet.py
	seqsift/seqops/seqstats.py

Merging changes to `summarize_distances` function of `seqstats` module
and the `seqvet.py` script.