Add SampleView.update_sample_metadata(), plus a test

[mattmcdermott]

Summary

Added a function for updating a Sample's metadata via the SampleView class.

This is introduced so that we can include metadata from tasks in the sample database. See #56

• Code is in the standard Python style.
  The easiest way to handle this is to run the following in the correct sequence on
  your local machine. Start with running black on your new code. This will
  automatically reformat your code to PEP8 conventions and removes most issues. Then run
  pycodestyle, followed by flake8.
• Docstrings have been added in theNumpy docstring format.
  Run pydocstyle on your code.
• Type annotations are highly encouraged. Run mypy to
  type check your code.
• Tests have been added for any new functionality or bug fixes.
• All linting and tests pass.

[mattmcdermott]

I'm going to merge this in myself since it doesn't affect any other features and all tests pass :) and I also need it right now to work on alab_one haha