Update opacity when disabled prop is changed

fixes #17105

If you render

```
    <TouchableOpacity
        disabled={true}
        style={{opacity: 0.5}}
    >
        ...
    </TouchableOpacity>
```

and then

```
    <TouchableOpacity
        disabled={false}
        style={{opacity: 1}}
    >
        ...
    </TouchableOpacity>
```

The content of `TouchableOpacity` will still have opacity = 0.5 because real
opacity is controlled by animated property which should be properly updated
when `disabled` prop changes.

Libraries/Components/Touchable/TouchableOpacity.js

@@ -162,6 +162,12 @@ var TouchableOpacity = createReactClass({
     ensurePositiveDelayProps(nextProps);
   },
 
+  componentDidUpdate: function(prevProps, prevState) {
+    if (this.props.disabled !== prevProps.disabled) {
+      this._opacityInactive(250);
+    }
+  },
+
   /**
    * Animate the touchable to a new opacity.
    */