Add .cb to SameDuck standard load file extensions

[suspect15]

Is your feature request related to a problem? Please describe.
SameDuck core (Mega Duck's core) only looks for .bin files when loading games, however .cb files are also supported by the core. The console was known as both Mega Duck and Cougar Boy and rom files can be in either .bin or .cb.

Describe the solution you'd like
Add .cb files to the default supported file extensions so when you select Load Game and the file selection window appears, .cb files can be selected without having to first select "All files ." in the bottom right