Track size of scoreboard image data

[JohnStrunk]

The scoreboard image is currently sent as a PNG to the CC, but if the user has a detailed background (i.e., a picture), the resulting PNG may be quite large, causing a delay while the CC loads it.

• Add monitoring of the image size
• Investigate the use of webp for the image format (lossy or lossless)
• Investigate dynamically switching to JPG if necessary