Customizable navbar height

[brentvatne]

Should be possible to specify navbar height in route config, right now the option is there but we aren't using it.

[juellez]

Not sure if it was an appropriate way to do it, but I set height: xx in defaultRouteConfig and it worked for me. e.g.

defaultRouteConfig={{
  navigationBar: {
    height: 70
...

[kay-es]

there is an invisible overlay (which is just as high as the initial navigation bar) if I set the height for the navigationBar this way :/