Backfill UIWebView tests

This adds `WebViewTests`, which backfills the following tests:
* Validating text in a `UIWebView` is visible
* Tapping an anchor in a `UIWebView`
* Typing into a `UIWebView`'s text input form field

I'm using these as a baseline to test `WKWebView` (if that's even possible) and figured it would be good to add to the source repo. I also think there is value for new KIF users seeing `UIWebView` testing in action.

Note: These tests make use of local HTML files to render content so they are not dependent on having an active network connection.