DO NOT MERGE: Issue 2106: Live Preview Snapshot

This is a PR for issue #2106.
Note:
Since all of the objects that use the WPAuthenticatedSessionWebViewManager check if several `UIWebViewDelegate` methods are implemented, perhaps, it would be simpler to expose the implemented method signatures here, and nuke all of the checks, such as:

```
    if ([self.authenticatedWebViewManager respondsToSelector:@selector(webView:shouldStartLoadWithRequest:navigationType:)]) {
         shouldStartLoad = [self.authenticatedWebViewManager webView:webView shouldStartLoadWithRequest:request navigationType:navigationType];
      }
```