Fixed text background color

Summary:
@public

This fixes an issue with the containerBackgroundColor property of `<Text>` nodes, where containerBackgroundColor was being overridden by the backgroundColor. I also fixed up the example so that it demonstrates the feature more clearly.

Test Plan:
* Check UIExplorer text example
* Run Catalyst snapshot tests and check MAdMan, Groups

Examples/UIExplorer/UIExplorerBlock.js

@@ -77,13 +77,7 @@ var styles = StyleSheet.create({
     paddingHorizontal: 10,
     paddingVertical: 5,
   },
-  titleRow: {
-    flexDirection: 'row',
-    justifyContent: 'space-between',
-    backgroundColor: 'transparent',
-  },
   titleText: {
-    backgroundColor: 'transparent',
     fontSize: 14,
     fontWeight: '500',
   },
@@ -101,8 +95,7 @@ var styles = StyleSheet.create({
     height: 8,
   },
   children: {
-    backgroundColor: 'transparent',
-    padding: 10,
+    margin: 10,
   }
 });