Add global keybinding helper

[glortho]

See #68 for details.

[sheldonrong]

hey @glortho do you mind have a quick check on PR #71 ?

I basically added a config option and if global is set to true, the key binding will be effective even the component is not focused.

[glortho]

Sorry for the delay @sheldonrong. Thank you for doing this! I'm on crazy deadline this week but will check it out ASAP.

[sheldonrong]

@glortho not a problem, send me a message when you are free to look at the PR :)