Allow BottomNavigation with no badges on icons

[leoparis89]

Enables the use of BottomNavigation with no badges. In the present state, is you put an empty string for a badge like this:

{
    "key": "account",
    "title": "account",
    "icon": "credit-card",
    "color": "blue",
    "badge": "",
    "accessibilityLabel": "myLabel",
    "testID": "myId",
  }

You get this unwanted behavior:

Now you can just do

{
    "key": "account",
    "title": "account",
    "icon": "credit-card",
    "color": "blue",
    "badge": None,
    "accessibilityLabel": "myLabel",
    "testID": "myId",
  }

  {
    "key": "account",
    "title": "account",
    "icon": "credit-card",
    "color": "blue",
    "badge": Some("33"),
    "accessibilityLabel": "cool",
    "testID": "myid",
  }

Also put option type on the other non mandatory route props.