Add Pegasus Frontend

[kewalsky]

Pegasus is a frontend launcher for game emulators (such as those currently in bucket)

• Files are distributed via GitHub
• Placing "portable.txt" in the application root will cause it to run in portable mode (docs)
• Portable mode configuration files are located in "/config" in the applcation root (docs)
• Possible manifest would create and persist the portable.txt and config folder

[kewalsky]

this might also be more fitted for Scoop Extra, not confident on which one it fits in better

[FlawlessCasual17]

Done in #711