added expandOnVisible

[alexookah]

I had an issue where i was showing a full screen image and when closed the navbar would automatically expand because of the notification DidBecomeVisible.

I see that you have a boolean value DidBecomActive and i thought it might be useful for someone else to have control and disable DidBecomeActive not to show the navbar from default.

hope this gets merged :)

Thanks for your awesome library

[alexookah]

@andreamazz

if expandOnVisible { showNavbar(animated: false) }

should this be without animated: false?

[andreamazz]

Hi @Alexookah thanks for the contribution. I think we should keep the default true value for the expandOnVisible path.

[alexookah]

@andreamazz ok made it default :)

[andreamazz]

Awesome, thanks!