Document topBar.height and title.height style option

docs/docs/styling.md

   modalPresentationStyle: 'overCurrentContext', // Supported styles are: 'formSheet', 'pageSheet', 'overFullScreen', 'overCurrentContext', 'currentContext', 'popOver', 'fullScreen' and 'none'. On Android, only overCurrentContext and none are supported.
   topBar: {
     visible: true,
+    height: 70, // Android only, optional; Height of the TopBar in dp.
     leftButtons: [{
       id: 'buttonOne',
       icon: require('icon.png'),
       fontSize: 14,
       color: 'red',
       fontFamily: 'Helvetica',
+      height: 70, // Android only, optional; Height of the TitleBar in dp.
       component: {
         name: 'example.CustomTopBarTitle',
         alignment: 'center'