Replace reST user guide with Jupyter Notebook for image quality guide, remove unused images

[hakonanes]

Signed-off-by: Håkon Wiik Ånes hwaanes@gmail.com

Description of the change

• Replace reST user guide file with Jupyter Notebook for image quality guide, using the kikuchipy.data.nickel_ebsd_large() dataset (from kikuchipy-data).
• Remove unused documentation images, since these are now generated from the notebook 🎉
• Changelog updated.

Progress of the PR

• Docstrings for all functions
• Unit tests with pytest for all lines
• Clean style in as per black

For reviewers

• Check that the PR title is short, concise, and will make sense 1 year
  later.
• Check that new functions are imported in corresponding __init__.py.
• Check that new features, API changes, and deprecations are mentioned in
  the unreleased section in doc/changelog.rst.