Add zone axes to geometrical EBSD simulations, improve plotting of simulation features

[hakonanes]

Description of the change

This PR concludes the basic functionality of simulations of geometrical EBSD patterns.

• Add zone axes attribute to the GeometricalEBSDSimulation class. These are calculated from the cross product of the present Kikuchi bands, and can be plotted along with the bands.
• Default Kikuchi band coloring using the color palette from EDAX TSL. The user can provide custom colors if desired.
• PC plotting is fixed, ensuring that only one PC is plotted per pattern
• Which zone axes to plot can be set in two ways: (1) on the detector, and (2) within a gnomonic radius (of course centered on the PC). Default is to exclude zone axis outside the detector
• Plotting of zone axes labels is updated, however, a warning is raised before plotting, see this pending HyperSpy PR for details: Add visibility boolean for all markers, only used by text markers hyperspy/hyperspy#2558
• Some routines for getting which HKL family a certain HKL belongs to are added as private functions in the geometrical simulation script. The extra functionality in these functions should be added to the already existing diffsims.crystallography.ReciprocalLatticePoint.unique() method.
• KikuchiBand and ZoneAxis __getitem__() methods are added. These should also, I think, be moved to ReciprocalLatticePoint.__getitem__().

Progress of the PR

• Docstrings for all functions
• Unit tests with pytest for all lines
• Clean style in as per black
• Test it all for signal navigation dimensions 0, 1 and 2 (coverage should be 100% after this PR)
• Jupyter Notebook showing how to simulate geometrical EBSD patterns and plot them as markers. This notebook should be placed in doc/notebook.ipynb and included in the user guide with nbsphinx (https://nbsphinx.readthedocs.io/en/0.7.1/index.html) will do this in a later PR.

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.