ps2: AltGr, change keymap through command (ps2 scheme)

Using keymap <file>, (MR: extrautils!43 (closed)) where <file> has syntax similar to xmodmap in Linux, you can change the keymap.

Also includes support in ps2 for escaped scancodes; in particular AltGr.

Extra keycodes are allocated in orbclient (MR: orbclient!58 (merged)) for the numpad, which allows for configuring keymap for those keys. This is how it is done in Linux, but of course it is up for discussion what we want to do. To accommodate the extra numpad keycodes, the keymap array is divided into 2 parts, because I had to use keycodes 0x70 and up for numpad keys. In Ps2d, numlock = true by default right now. Not yet support for Num Lock button. The keymap array has 4 columns right now but that could be made 3 maybe, if we don't care about shift + AltGr combo.