Expand visual testing logs with a side-by-side comparison

Expand visual testing logs with a side-by-side comparison

• Add a baseline.png image to the ./latest_logs/ folder on visual diff failures.
• Add a baseline_diff.png image to the ./latest_logs/ folder on visual diff failures.
• Add a side_by_side.html file showing both of the above images together on visual diff failures.
• Give the new side_by_side.html file a nice favicon.
• Make updates to the visual_baseline/ folder:
  -- Rename screenshot.png to baseline.png.
  -- Add latest.png to help the user detect important changes to the existing visual baseline.
• Here's an example of a side_by_side.html file from ./latest_logs/:

• See SeleniumBase/examples/visual_testing/ReadMe.md for complete instructions.
• Or see the Docs page: https://seleniumbase.io/examples/visual_testing/ReadMe/

Also:

• Improve output for deferred asserts:
  -- (For when the user forgets to call self.process_deferred_asserts() before the end of tests.)
• Refresh Python dependencies:
  -- parso==0.8.3;python_version>="3.6"