Add feature to create installer dmg

[Dave Lebbing]

The info popover near "Select macOS Installer Disk Image" that provides instructions on how to create a dmg with a macOS installer may be better if refactored into a button like "Create Bootable Volume". And if possible, to provide ability to copy prepared Terminal command to clipboard, or to execute command directly.

[timothy perfitt]

I don't like this interface much. Need to rework UI. Hodling