Backport the 7zFM GUI to win32s or win386

[dajhorn]

Retro7zip lacks the file manager that is in the upstream 7-Zip release.

Two potential solutions are:

1. Rewrite the user interface for the watcom resource compiler and build using the win386 extender.

This would make Windows 3.0 the oldest Windows platform supported by retro7zip and keep the entire project in Open Watcom v2.

2. Patch-down the in-tree resource files to the win32s level and build 7-Zip GUI components using Microsoft Visual C++ 2.

This would make Windows 3.1 the oldest Windows platform supported by retro7zip.

As a side-effect, this would also make an Apple Macintosh build for Classic Mac OS 7 doable using the Microsoft Visual C++ 2.0 Cross-Development Edition for Macintosh.