Add option to show notification popups when app is in foreground

[patrykmol]

Problem description

Currently it is not possible for developer to configure presentation of notification popups.

Expected behavior

Developer should have control over how the notification is presented when app is in foreground.

We should introduce a property like showBannersInForeground (boolean) that will allow to change this behaviour.

[patrykmol]

This is implemented for iOS.

[mpost]

@patrykmol Could you create the corresponding js implementation and documentation?

[patrykmol]

@mpost Sure.