* Update WebView.ios.js

* Update WebView.ios.js

fixes #29
fixes #272
fixes #221
fixes #105
fixes #66

BREAKING CHANGE: Communication from webview to react-native has been completely rewritten. React-native-webview will not use or override window.postMessage anymore. Reasons behind these changes can be found throughout so many issues that it made sense to go that way.

Instead of using window.postMessage(data, *), please now use window.ReactNativeWebView.postMessage(data).

Side note: if you wish to keep compatibility with the old version when you upgrade, you can use the injectedJavascript prop to do that:

const injectedJavascript = `(function() {
  window.postMessage = function(data) {
    window.ReactNativeWebView.postMessage(data);
  };
})()`;

Huge thanks to @jordansexton and @KoenLav!

Added a new cacheEnabled prop to toggle Android & iOS webview caching behavior.

BREAKING CHANGE:  This change makes caching enabled by default when previously there was no caching behavior which may cause unexpected behaviour changes in your existing implementations.

Allows the webview to be opened with an ephemeral data storage.

* fix(WKWebview): [iOS] Add shared process pool so cookies and localStorage are shared across webviews (#68)

* Add optional shared process pool

BREAKING CHANGE: useSharedProcessPool prop is set to true by default. If you want the old behavior, please use useSharedProcessPool={false}

This PR adds support for `onShouldStartLoadWithRequest` on android.

The initial PR was #59

The issue for this PR is: #106

fixes #106

* [ios] Add ‘allowsLinkPreview’ property to iOS WKWebView.

* Add divider in docs

* Typo: add hyphen -> _allowsLinkPreview

Fixes #33 

I could really use some help from an Android developer on this one, because I just "made it work", don't know how to "make it work good".

Some things that should be reviewed:

- [ ] validate Android 5.0 devices (my emulator work, but outputs some weird sounds; a Galaxy 4 I tested on crashes)
- [ ] validate Android 5.1 devices (emulator works, couldn't find a real device)
- [ ] how to handle File Extensions? (https://www.w3schools.com/tags/att_input_accept.asp)

I'm sure that there's more refactoring to be done, so any help and advice would be appreciated.

* Add 'userAgent' property to the iOS WKWebView

* Update 'userAgent' reference docs.

* add hideKeyboardAccessoryView option

* add hideKeyboardAccessoryView prop to reference

* Added the onLoadProgress property to the iOS wkwebview and Android webview