[user friendly feature] Add ability to specify a label to the shortcut

[Marino Simic]

Please add ability to specify a label when registering a shortcut:

hotkeys(shortcut: string, scope: string, func: Function, label: string)

so that we can list them with

hotkeys.getAllKeyCodes()

and present to the user the label of what the shortcut does.

This should be trivial to implement, hopefully.