Small finishing touches added to explore_bag_data.ipynb file

[ethanhu912]

Description

• Resolves Pathfinding data plotting workflow #753
• Made some small changes to explore_bag_data.ipynb
• Created a helper functions cell and moved all repeated functions to that cell
• Removed the code that opened the same database in each cell (so it's only opened once at the start)
• Standardized all calculations to units in kilometers and seconds

Verification

• Ran each code cell to ensure the same functionality as before
• Verified that the cell returned values in km/h

[SPDonaghy]

Hi Ethan! Sorry cant really review this properly as the diff for an ipynb file is practically unreadable. If everything looks good/works for you we can merge this. The notebook can just serve as a good place to test things out but I wont look at the code in them too closely. We can review the code for the actual script (that presumably does the things the cells in the nb do) a bit more closely once that's ready.