* add define for SDL_SCANCODE_GRAVE - seems like only SDL2
has names for the values
* add some missing keys to SDL_KeyToDoom3Key
* add scancode to unmapped-key warning
* backspace needs to be handled the same for SDL1 as in SDL2
(i.e. a new event must be created for it) to work in console
* Add support for Console-Key independently of KB Layout (with scancode)
* add support for TAB key
* Add hack so console is empty after opening it (SDL-only)
it didn't work correctly because the mouse isn't grabbed
(in contrast to dhewm3).
It's fixed now by returning absolute coordinates when a menu
is open, furthermore the cursor is now always hidden.
