Remove legacy keymap support
Merge tr_init and vid_sdl2. Some refactorization done

vid_conwidth and vid_conheight now default to 0, they depend on the
window resolution and use width/2, height/2 as default and will be
redrawn upon resizing window (if not user has specified a value).
Remove redundant key events for special keys (patch from hifi)
Add missing ISO key (patch from hifi)