fix(WKWebview Scroll): Don't allow the scrollView to scroll when `scrollEnabled={false}`. (#158)

* Don't allow the scrollview to scroll the WebView body.

* Readme comment

* Remove duplicate protocol def

docs/Reference.md

 
 ### `scrollEnabled`
 
-Boolean value that determines whether scrolling is enabled in the `WebView`. The default value is `true`.
+Boolean value that determines whether scrolling is enabled in the `WebView`. The default value is `true`. Setting this to `false` will prevent the webview from moving the document body when the keyboard appears over an input.
 
 | Type | Required | Platform |
 | ---- | -------- | -------- |

ios/RNCWKWebView.m

 {
   _scrollEnabled = scrollEnabled;
   _webView.scrollView.scrollEnabled = scrollEnabled;
+
+  // Override the scrollView delegate to prevent scrolling.
+  if (!scrollEnabled) {
+    _webView.scrollView.delegate = self;
+  } else {
+    _webView.scrollView.delegate = _webView;
+  }
+}
+
+- (void)scrollViewDidScroll:(UIScrollView *)scrollView
+{
+  // Don't allow scrolling the scrollView.
+  scrollView.bounds = _webView.bounds;
 }
 
 - (void)setShowsHorizontalScrollIndicator:(BOOL)showsHorizontalScrollIndicator