**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
c = base::ToLowerASCII(c);
  *shifted = false;
  switch (c) {
    case 0x08:
      return ui::VKEY_BACK;
    case 0x7F:
      return ui::VKEY_DELETE;
    case 0x09:
      return ui::VKEY_TAB;
    case 0x0D:
      return ui::VKEY_RETURN;
    case 0x1B:
      return ui::VKEY_ESCAPE;
    case ' ':
      return ui::VKEY_SPACE;
    case 'a':
      return ui::VKEY_A;
    case 'b':
      return ui::VKEY_B;
    case 'c':
      return ui::VKEY_C;
    case 'd':
      return ui::VKEY_D;
    case 'e':
      return ui::VKEY_E;
    case 'f':
      return ui::VKEY_F;