Dark mode compatible image in rich text items

[mathebox]

Is your feature request related to a problem? Please describe.
User-uploaded (teaching team) images in rich text items, might be designed for light mode only. Those images can look out of place in dark mode.

Describe the solution you'd like

1. Identify images: Only images with a white background (main color) or a translucent background should be considered.
2. Apply CIFilter named CIColorInvert to invert images.

Affected Component
HTMLStyler

Additional context
Get the main color of an image: https://stackoverflow.com/questions/41552544/getting-main-colors-of-a-uiimage-in-swift