**Is your feature request related to a problem? Please describe.**
The Caps Lock and Fn keys are useful to some, and not others. I would greatly enjoy being able to use these keys as modifiers for something more useful to me.

**Describe the solution you'd like**
Add global shortcuts support for the cap locks and fn keys. While these keys are not useless and are not proper modifier keys, I feel that the design choice should be left to the app developer.

**Describe alternatives you've considered**
The only alternative would be to use a keypress listener/sender to 'remap' the key to something Electron supports; or substitute electron's shortcut functionality completely.

**Additional context**
Using a 3rd party keypress listener does not feel safe.
atom/common/keyboard_util.cc
case 'g':
      return ui::VKEY_G;
    case 'h':
      return ui::VKEY_H;
    case 'i':
      return ui::VKEY_I;
    case 'j':
      return ui::VKEY_J;
    case 'k':
      return ui::VKEY_K;
    case 'l':
      return ui::VKEY_L;
    case 'm':
      return ui::VKEY_M;
    case 'n':
      return ui::VKEY_N;
    case 'o':
      return ui::VKEY_O;
    case 'p':
      return ui::VKEY_P;
    case 'q':
      return ui::VKEY_Q;
    case 'r':
      return ui::VKEY_R;
    case 's':
      return ui::VKEY_S;
    case 't':
      return ui::VKEY_T;
    case 'u':
      return ui::VKEY_U;