Installer improvements

[corbindavenport]

The current installer can format disks and copy a core DOS system, but more features should be implemented.

• [ ] Avoid wiping target drive by default
• [x] Install core utilities to C:\SYSTEM directory (#1)
• [ ] Detect existing DOS systems and installing over them (keep the kernel, replace everything else)
• [ ] Detect virtual machines and show tips (e.g. changing sound card on VirtualBox)
• [ ] Create separate USB installation image that doesn't rely on floppy emulation (maybe using GRUB2?)

[corbindavenport]

Might have to use GRUB4DOS: https://www.wikka.puppylinux.com/Grub4Dos