Android: slow navigation

Browsing is quite slow on both the emulator and device, yet it seems to depends because sometimes it feels OK...

We need to check the animations in general as it is known that they can be an issue on Android.

There is a lot to read about this subject in https://facebook.github.io/react-native/, https://github.com/facebook/react-native and StackOverflow.

Note that this doesn't seem to be related to react-native-router-flux as it is only a wrapper of NavigationExperimental, see https://github.com/aksonov/react-native-router-flux/issues/355#issuecomment-199704310.