Updating `get_translation` function.

Updating `get_translation` function of `sequtils` module. Fixing check
for `translate` attribute. Also, adding the stripping of extra bases
(i.e., any bases at the end of the sequence that are not a triplet)
before `translate` method is called.
Adding tests to `test_sequtils.py`.

Adding tests of `copy_seq_metadata`, `get_without_gaps`, and
`get_translation` functions.

All are passing.
Updating `seqmod` module.

Importing `sequtils` module rather than specific functions from the
module, and updating `seqmod` functions accordingly.

Also, updating `translate_seqs` function to call
`sequtils.get_translation` on each sequence.
Adding tests of `translate_seqs` function.

Adding tests of `translate_seqs` function to `test_seqmod.py`.  Also
importing `seqmod` module within `test_seqmod.py` rather than importing
everything via wildcard (*).

All tests are passing.