Add ability to label plugins in sidebar by color

[sibir-ine]

Slice asked in the Discord for the ability to add color labels to plugins in the sidebar to better track & organize them. For the organization aspect, this could potentially be combined with #1758 (e.g., allowing the user to change the color of the icon from the interface & store it per-plugin). For the tracking aspect, it might be worth taking a look at #377 again as a better solution.