* Add `onScroll` callback for iOS & Android

This code was mostly extracted from https://github.com/react-native-community/react-native-webview/pull/202

I tried and tried to make it work with `Animated.event`'s `useNativeDriver`, but I was unsuccessful 😢 that'll have to be done later once I understand better how Animated's native stuff is hooked up.

* fix crash for missing onScroll

* [iOS] Allow focus without user interaction

* Add documentation for keyboardDisplayRequiresUserAction

* set keyboardDisplayRequiresUserAction default to true

WebViewProgressEvent musst be wrapped within NativeSyntheticEvent

We had the problem on iOS WebViews that local cookies (stored in local HTTPCookieStorage, set with  [react-native-cookie](https://github.com/shimohq/react-native-cookie) ) were not added in loadRequests. On Android the local stored cookies were sent like expected.
This kinda "hacky" solution is the only way we found, that works for us.
The stack overview link is in the code below.
If someone finds a better solution we would very much like to accept that.

When setting a custom font size in the Android system, an undesirable scale of the site interface in WebView occurs.

I researched that when setting the standard textZoom (100) parameter size, this undesirable effect disappears.

This can be very useful if you need to avoid the scale of content in WebView when changing the size of system fonts, or change textZoom property directly.

Example:

`
<WebView
  textZoom={100}
/>
`

Rewrote the whole repository into typescript. This will provide way better and up to date documentation. This should also add some safety for people contributing 😄 .
Flow types were not working until now which is why this PR doesn't have them but feel free to PR.

This also fixes #384 #435 #206 #171 #168.

fixes #304

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.

* add test code for disable hardware acceleration

* add interface to disable android hardware acceleration

* Update index.d.ts

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

* 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