Fix broken formatting: reformat everything with black

[mruffalo]

The code formatting in SnapTools has some issues. This is not a stylistic opinion -- parts of the package are broken due to code formatting. Specifically, mixing tabs and spaces for indentation is not permitted under Python 3, which makes some parts of the code impossible to run (or even import):

Python 3.8.2 (default, Apr 27 2020, 15:53:34)
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import snaptools
>>> snaptools.__version__
'1.4.8'
>>> from snaptools.alignment import filter_fastq
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/mruffalo/.opt/python3.8-venv/lib/python3.8/site-packages/snaptools/alignment.py", line 79
    print("error: no barcode is selected")
                                         ^
TabError: inconsistent use of tabs and spaces in indentation

It isn't a good use of anyone's time to fix code formatting by hand, and everyone has a slightly different opinion about good style. Let's be neutral and defer to the black code formatter: https://pypi.org/project/black/