Deprecate instead of removing three chunk processing functions

[hakonanes]

Description of the change

Reintroduce the kikuchipy.pattern.chunk functions remove_static_background(), remove_dynamic_background() and get_image_quality(), which were removed in #527. Better to deprecate and remove in v0.7.

Progress of the PR

• Docstrings for all functions
• Unit tests with pytest for all lines
• Clean code style by running black via pre-commit

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• New functions are imported in corresponding __init__.py.
• New features, API changes, and deprecations are mentioned in the unreleased
  section in CHANGELOG.rst.
• New contributors are added to .all-contributorsrc and the table is regenerated.