Add EBSD.xmap class property storing a CrystalMap, read from EMsoft EBSD file

[hakonanes]

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

Description of the change

• Add EBSD.xmap class property storing a CrystalMap
• Read orientations and phase information from EMsoft simulated EBSD file into this xmap property
• Add short note in IO user guide

Must be added in other PRs:

• Make property setable
• Slice xmap when slicing a signal using s.inav[]
• Read this info from TSL/Bruker h5ebsd files.

This was added quickly now because @onatlandsmyr needs it.

The _crystaldata2phase() IO function should be moved to orix.io.plugins.emsoft_h5ebsd.

Progress of the PR

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

Minimal example of the bug fix or new feature

>>> import kikuchipy as kp
>>> s = kp.load("my_data.h5")
>>> s.xmap
Phase  Orientations  Name  Space group  Point group  Proper point group     Color
    0  200 (100.0%)    ni        Fm-3m         m-3m                 432  tab:blue

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.