Improvement to landscape plots, MCMC summary, x0 log entry

[BradyPlanden]

Description

• Updates to MCMC summary class
• Update to contour and surface plots
• Adds x0 as optim.log entry

Issue reference

Fixes #235

Review

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• Updated the CHANGELOG.md in reverse chronological order (newest at the top) with a concise description of the changes, including the PR number.
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[BradyPlanden]

Below are the updated landscape plots, the following changes have been made:

• The optimisation trace colouring has been changed to greyscale
• The contour colourscale has been changed to Viridis to align with the surface plot
• Initial and final values are added via crosses (colour matching the optim trace) with entries in the legend.

Open to suggestions for improvements, just drop a comment 😃

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.15%. Comparing base (c8b00e6) to head (8c6c8f9).
Report is 26 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #570      +/-   ##
===========================================
+ Coverage    99.08%   99.15%   +0.07%     
===========================================
  Files           52       56       +4     
  Lines         3605     3918     +313     
===========================================
+ Hits          3572     3885     +313     
  Misses          33       33              

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