Several bug fixes;
Preliminar addition of the SDL 2 renderer (does not yet work correctly in full screen mode);
SCSI devices no longer have configurable LUN's (this matches the configurability of real SCSI devices);
SCSI LUN's are now handed by the device's handler;
Removed all unused strings;
Removed some unused code files;
Significantly rewrote the bus mouse emulation.
Turned the char arrays in gameport.h into const char pointers;
The makefile no longer links in the (unfinished) PIIX4 emulation code (which is currently not used by anything even in the Dev branch).
Applied all the video-related PCem commits;
The keyboard ALT+TAB detection now sends one extra ALT key down and up, so the guest does not get stuck in a menu bar.
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.
