Mph plots

[camisowers]

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What is the purpose of this PR?

Closes #87.
Create an example notebook for MPH plots that updates the x-axis to use cumulative total counts for each FOV.
Also is watcher compatible.

Remaining issues

Any formatting fixes or plot design.
The combined csv for all the data has pulse_heights and cum_total_count and stored. If we also want the individual total_counts and/or the FOV number included I can add those as well.

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[ngreenwald]

It looks like the functionality is all here. However, the goal of the notebooks is to have a clean interface for the user to work with. This means abstracting all of the main code into helper functions that are called. This also allows the code to be re-used by the watcher functions. However, this notebook has everything in individual cells

[camisowers]

I need to add some kind of error or warning for if the CSVs already exist. We could just pull the data from those or compute the mphs again to be safe and overwrite with new files.
I'll also get started on tests.

[ngreenwald]

Nice job pulling out the logic into functions. Some comments about how to make these functions compatible with the watcher

[ngreenwald]

Almost there!

[camisowers]

The updated watcher notebook was tested against data from creed and ran smoothly.

[ngreenwald]

Looks good, just some final cleanup

[camisowers]

will update the image extraction notebook name and readme link in PR #130