Key bindings names in the settings menu are layout-specific

When I start OpenMW with a Russian keyboard layout, I see such key names in the settings menu on Linux:

On Windows these is a mix of Latin and Cyrillic characters instead:

The problem is that we get names from key codes, but they depend on keyboard layout and current platform.

A suggested solution is to use SDL_GetScancodeName instead of SDL_GetKeyName - we map scan codes to input bindings anyway.