Reined back over-use of virtual functions in GHOST, especially in
"leaves" of the inheritance hierarchy. This eliminates vtables for many
classes and (in some places) turns virtual function dispatch into direct
function calls.
I'll be around to fix things if other coders think this change is too
much.
Still lots of virtual in GHOST_TaskbarWin32 since it just loves virtual.
GHOST*Cocoa.mm & .h files creation
First Cocoa version of GHOST_SystemCocoa.mm
CMake files update to allow optional (WITH_COCOA option) Cocoa version build - disabled by default
SCons files are not updated to allow Cocoa build (the ghost .mm files)
