Add tabBarTranslucent style option in tabsStyle (#999)

Add tabBarTranslucent style option in tabsStyle

docs/styling-the-tab-bar.md

   tabBarButtonColor: '#ffff00', // change the color of the tab icons and text (also unselected)
   tabBarSelectedButtonColor: '#ff9900', // change the color of the selected tab icon and text (only selected)
   tabBarBackgroundColor: '#551A8B' // change the background color of the tab bar
+  tabBarTranslucent: false // change the translucent of the tab bar to false
   tabBarTextFontFamily: 'Avenir-Medium' //change the tab font family
 }
 ```
   appStyle: {
     tabBarBackgroundColor: '#0f2362',
     tabBarButtonColor: '#ffffff',
-    tabBarSelectedButtonColor: '#63d7cc'
+    tabBarSelectedButtonColor: '#63d7cc',
+    tabBarTranslucent: false,
     tabFontFamily: 'Avenir-Medium.ttf'  // for asset file or use existing font family name
   },
 ...
 }
 ```
 
-All supported styles are defined [here](https://github.com/wix/react-native-controllers#styling-tab-bar). There's also an example project there showcasing all the different styles.
+All supported styles are defined [here](https://github.com/wix/react-native-controllers#styling-tab-bar). There's also an example project there showcasing all the different styles.

ios/RCCTabBarController.m

       UIColor *color = tabBarBackgroundColor != (id)[NSNull null] ? [RCTConvert UIColor:tabBarBackgroundColor] : nil;
       self.tabBar.barTintColor = color;
     }
+
+    NSString *tabBarTranslucent = tabsStyle[@"tabBarTranslucent"];
+    if (tabBarTranslucent)
+    {
+      self.tabBar.translucent = [tabBarTranslucent boolValue] ? YES : NO;
+    }
   }
   
   NSMutableArray *viewControllers = [NSMutableArray array];