Improve MacOS Experience

This one is more minor, just a UX improvement. It would be cool to have the native minimize, close window and quit options (cmd + q) work on a Mac. Rather than...

I'm recommending we leverage what most other MacOS apps look like, for example VSCode...

... with the standard red close, yellow minimize and green maximize buttons.

Not sure what this entails within Electron but I'd be surprised if it's not doable. I've always been interested in Electron and would be happy to take a stab at this though. We need to be careful not to let this improvement break things on the other supported operating systems.

Also, related to cmd + q not working, I see something other than the usual "Quit [App Name]" option in the file menu...

@dsheiko was there some rationale as to not going with the native options? Maybe Electron doesn't make them easy to do natively across platforms?

Looks like it's just because we're using a frameless window here...

https://github.com/dsheiko/puppetry/blob/master/app/main.js#L60

I did it so back then because on Windows it looked quite ugly, but you have a point. I'll consider to change it