Summary:
Allows setting of HTML directly on webview to support #506. This is a starting point, and feedback/improvement is requested.
1. if `startInLoadingState` is true, the HTML content will never show since the load event never fires
2. Neither html nor url are set as required props any more
Closes https://github.com/facebook/react-native/pull/542
Github Author: Colin Ramsay <colinramsay@gmail.com>
Test Plan: Imported from GitHub, without a `Test Plan:` line.
4b4e8ecc9b