Attach empty onclick listener to each node

Fixes #1169.

This is a more robust way of fixing what MobileSafariClickPlugin previously tried to. Now even if you don't want anything to do with touch events, click events still work properly.

Test Plan: Added a click handler to an `<img />` element and triggered it in the iOS simulator -- it didn't execute before.
Merge pull request #1536 from spicyj/gh-1169

Attach empty onclick listener to each node