Fix binding 'context menu' key using SDL2

SDL 1.2 converted Windows' VK_APPS and X11 XK_Hyper_R to SDLK_MENU.
SDL2 has it as a separate SDLK_APPLICATION key, so convert it to K_MENU too.
Fix Windows key bind name on non-Mac using SDL2

SDL 1.2 sends SDKL_*META (command) and SDLK_*SUPER (windows key).
SDL2 sends SDLK_*GUI for both.
Merge remote-tracking branch 'ioquake3/master'