**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
#include <string>
#include "atom/common/keyboard_util.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_util.h"
#include "third_party/blink/public/platform/web_input_event.h"
#include "ui/events/event_constants.h"
namespace atom {
namespace {
ui::KeyboardCode KeyboardCodeFromKeyIdentifier(const std::string& s,