Select ColPic for format of g-code thumbnails.

Some versions of Moonraker in the Elegoo distributed firmware distributions have issues displaying thubnails on the side microcontroller Display and/or in Fluidd. Sometimes this is seen using Orca when Cura may work when using as the slicer. These issues are related to what thumbnail formats are included by the slicer and which are configured in Moonraker.

See https://github.com/VBitsHub/elegoo_moonraker for instructions for updating your Moonraker files