Replace reST with Jupyter Notebook for visualizing signal guide

[hakonanes]

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

Description of the change

• Replace reStructuredText file with Jupyter notebook for the signal visualization user guide
• Remove some images from the documentation (generated in the notebook by readthedocs)

Progress of the PR

• Docstrings for all functions
• Unit tests with pytest for all lines
• Clean style in as per black
• Find a nice colour image to turn into navigator for the kikuchipy.data.nickel_ebsd_large() dataset (orientation map? RGB orientation map?)
• Decide whether to use a GIF to show multiple scan plotting, or just a static inline plot. Further, include simulated patterns from EMsoft, or just the orientations and wait for Detector Pattern Simulation #239 and get the dictionary of simulated patterns ourselves?
• Changelog entry

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.