NB Improvements for issue/42/restore demos

[OliviaLynn]

Change Description

• For #52
• Improving notebooks in core/ and creation/

Solution Description

Making some improvements to notebooks (core and creation so far) for better readability, especially on RTD.

• Fixing use of headings to reflect conceptual hierarchies within the document (these show up on the RTD sidebar, so are important for navigation)
• Creating titles where missing; capitalizing all titles to title case for consistency across all notebooks
  • Chose title case based on MAST using that standard in their notebooks repository, too
• Removing <a> and <br> tags
  • These don’t work with nbconvert, and the anchor tags don't seem to work in GitHub previews or within my IDE
• Fixing references to old data locations, or to things in RAIL that are now in rail_base
• Deleting empty cells at end of notebooks

Code Quality

• [x] I have read the Contribution Guide
• [x] My code follows the code style of this project
• [x] My code builds (or compiles) cleanly without any errors or warnings
• [x] My code contains relevant comments and necessary documentation

Project-Specific Pull Request Checklists

Documentation Change Checklist

• [x] Any updated docstrings use the NumPy docstring format

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (db87923) 100.00% compared to head (51dcbb8) 100.00%.

:exclamation: Current head 51dcbb8 differs from pull request most recent head cbd148d. Consider uploading reports for the commit cbd148d to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #53 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 1 1 Lines 1 1 ========================================= Hits 1 1 ```

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