Bunch of improvements in the device, memory and MMU handling.
Re-worked the NEAT 286 chipset (ported from VARCem).
Re-worked the ATI 28800 a bit, added Sierra SC1502x ramdac to VGA Wonder XL (Compaq) since it supports such.
Top 384K memory handling improvements (256K top memory too)
Added MCA version of MPU-401 (not tested much, however).
Re-worked the SCAT 286 chipset.
Fixes to various hard disk controllers;
Added the Packard Bell PB640;
Fixed the InPort mouse emulation - now it works correctly on Windows NT 3.1;
Removed the status window and the associated variables;
Completely removed the Green B 486 machine;
Fixed the MDSI Genius;
Fixed the single-sided 5.25" floppy drive;
Ported a CPU-related commit from VARCem.
Merged floppy.c and fdd.c and renamed floppy_*.c (the floppy image format handlers) to fdd_*.c;
Reading the AT or PS/2 keyboard controller status no longer clears the transmit timeout bit, fixes error 8601 (mouse error) on the IBM PS/2 Model 80;
MMU translate and DMA physical reads and writes now go through _mem_exec instead of directly to ram[], should fix the last remaining problems with remapped mappings;
Implemented the Sound gain dialog;
Added the resource for the "New floppy image" dialog and the needed functions for the functionality of exporting the currently mounted floppy image as 86F, both of which should be finished in the next commit;
Applied the CD-ROM fixes from the PCem commit;
Added the "Keep ratio" option for full screen stretch.
IBM.H is gone, video stuff re-organized. Keyboard stuff reorganized.
Machines that have their own video, mouse and/or keyboard now have all this in their machine file.
Fixed and other cleanups here and there.
