React-native-navigation: [V2] Add support for navigate back event

[noamco]

Issue Description

Add support for navigate back event triggered by user pressing the back/up button, physical back button or swiping left.

[wbercx]

+1. Would be great to be able to intercept back button presses in v2, for showing confirmation modals etc. This is the only loss in functionality I've run into so far when moving from v1 to v2.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.
If you believe the issue is still relevant, please test on the latest version and report back. Thank you for your contributions.

[stale[bot]]

The issue has been closed for inactivity.

[angelos3lex]

Is this planned to be implemented sometime?

[jacobrosenskold]

Would really need this funktion as well.