To add an icon to this plugin:

1. Create a 64x64 pixel PNG image with a transparent background
2. Save it as "icon.png" in this directory (E:\dev\chisurf\chisurf\plugins\pch)
3. The icon will be automatically loaded when the plugin menu is populated

The icon should represent the functionality of the plugin, such as a histogram 
visualization for this Photon Counting Histogram plugin.

Once the icon is added, make sure the "icons_enabled" setting is set to true in 
settings_chisurf.yaml under the "plugins" section.