Menu for scripting

In this release of LosslessSwitcher,

A new menu has been added to allow for selected shell script to run, with the first argument being the latest sample rate.

Notes

• Selected shell scripts must have a shebang declared, such as #!/bin/bash
• The script will run when the app launches for the first time.
• The script file selection window may sometimes show underneath your current active window. (it's how macOS works)