Tweaks to accommodate new imaging setup

[tmcgrath325]

Fixes

• The GUI sometimes ran into indexing issues after pruning segments, as n segment labels don't necessarily overlap with 1:n

New features

• A calibration image can be provided for correction of uneven illumination
• If images are taken with the stimulus in a consistent location, its expected location can be used for assigning to it the correct spot
• Clunky buttons for adjusting the color similarity threshold on the fly. These could be changed to a text input for easier use, but these tend to be less necessary after doing illumination correction, so the buttons are Good Enough™ for now.
• Edges can now be cropped off of input images via keyword arguments when calling gui.

Tweaks

• Modified default values for color similarity thresholding and the minimum size for kept segments.
• Moved centroid calculation to its own function
• Updated docs images with ones that are representative of our current imaging setup

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.29%. Comparing base (bd67d50) to head (2fba6da).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #8      +/-   ##
==========================================
+ Coverage   97.54%   98.29%   +0.75%     
==========================================
  Files           4        4              
  Lines         244      293      +49     
==========================================
+ Hits          238      288      +50     
+ Misses          6        5       -1     

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[timholy]

Just wanted to say, thanks for the great summary and for getting these changes submitted & merged!