Slight reworking in the mouse and network code (ported from VARCem) in preparation for a major change that will const a lot of things to further reduce RAM usage.
Reduced sound gain options to one (because the per-source gain does not work right);
Added the Diamond SpeedStar PRO (CL-GD 5428), per patch from TheCollector1995.
The settings dialog now keeps track of MFM/XTIDE/ESDI/IDE channels and SCSI ID's and LUN's;
The IBM PS/2 Model 50 now installs a Model 80-style memory expansion card (MCA ID FCFF) when more than 2 MB RAM is selected, and now supports a maximum of 10 MB RAM.
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.
