Add support for local shortcuts

[curtisblackwell]

There's already support for global shortcuts, but not local shortcuts.

Would you merge a PR adding support for local shortcuts that follows the contribution guide?

[mpociot]

Yeah sure!

[curtisblackwell]

I was struggling with getting tests to pass in the NativePHP/electron-plugin and realized they were failing in the latest merge. Should I ignore tests in that repo for now?

[curtisblackwell]

I discovered I was incorrect. Local shortcuts are supported, they're just called hotkeys in the docs and they're on the Application Menu page. This makes sense since, as far as I can tell, Electron only supports local shortcuts connected to menu items.