Add --no-prefix global flag to remove command string from spawned output

[Blasz]

I've created a globalOptions singleton to store global flags to prevent passing args down everywhere.

I considered adding useBasename as an option as well but didn't think it would be useful enough for the end consumer to add as a flag. We only use it when executing yarn commands.

I also made some other yarn commands print basename and silenced the output of the user agent call we make.

[lukebatchelor]

LGTM

[lukebatchelor]

Released in 0.24.5