Update version number, changelog and notebooks for v1.6.0 release

[w-k-jones]

• Have you followed our guidelines in CONTRIBUTING.md?
• Have you self-reviewed your code and corrected any misspellings?
• Have you written documentation that is easy to understand?
• Have you written descriptive commit messages?
• Have you added NumPy docstrings for newly added functions?
• Have you formatted your code using black?
• If you have introduced a new functionality, have you added adequate unit tests?
• Have all tests passed in your local clone?
• If you have introduced a new functionality, have you added an example notebook?
• Have you kept your pull request small and limited so that it is easy to review?
• Have the newest changes from this branch been merged?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.53%. Comparing base (ca2f51d) to head (00b4510).

Additional details and impacted files

@@            Coverage Diff             @@
##           RC_v1.6.0     #495   +/-   ##
==========================================
  Coverage      63.53%   63.53%           
==========================================
  Files             27       27           
  Lines           3842     3842           
==========================================
  Hits            2441     2441           
  Misses          1401     1401           

Flag	Coverage Δ
unittests	63.53% <100.00%> (ø)

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[github-actions]

Linting results by Pylint:

Your code has been rated at 8.31/10 (previous run: 8.31/10, +0.00)
_{The linting score is an indicator that reflects how well your code version follows Pylint’s coding standards and quality metrics with respect to the RC_v1.6.0 branch.
A decrease usually indicates your new code does not fully meet style guidelines or has potential errors.}

[w-k-jones]

@freemansw1 @fsenf Let me know if this needs reviewing or if it can be merged straight away

[fsenf]

Thank you for preparing the release! I am fine with the changes, but did not review notebooks again. I am guessing they were just rerun. Please go ahead and merge!