add new option to control the contentMode in Android platform

Adds a transparentBackground option for iOS and Android

The 'open' method requires an options dictionary

iOS: Call setNeedsLayout() in scrollViewDidScroll()

This is useful to prevent a brief white flash on initialization
for apps that use a dark theme.

Otherwise, SwiftFlutterPlugin.swift throws an exception on line 285
when the InAppBrowser.openWithSystemBrowser(url) method is called:

  let options = (arguments["options"] as? [String: Any])!

Otherwise, the web view scrolls in blank white space which
doesn't get painted until the scroll gesture is finished,
because the WKWebView hasn't rendered that part of the
viewport to its offscreen buffer.

Add null checks around calls to InAppWebView callbacks

This prevents a crash I've been seeing as of v1.1.2 (for the onScrollChanged callback)
and should also prevent any other similar possible crashes.

Also, suppress an unused_field analyzer warning for InAppWebViewController._id.

fix #74, merge #81 #83, fix javascript `...args` parameter of `window.flutter_inappbrowser.callHandler()`

bug fix for android build

Enable setTextZoom function of Android-WebViewSetting

Android dependency 'androidx.core:core' has different version for the compile (1.0.0) and runtime (1.0.1) classpath

 Enable setTextZoom function of Android-WebViewSetting

updated documentation for addJavaScriptHandler method, updated README.md, updated inline webview example

added return value for JavaScriptHandlerCallback, added flutterInAppBrowserPlatformReady event for javascript, breaking change: javaScriptHandlersMap contains only one callback

upgrade to androidX

added support for iOS inline native WebView integrated in the flutter widget tree (#18, #45), fix #54 #38 #26 #32 #33 #29 #15

Fixed bug where passing null to expiresDate failed

[fix] encode resourceURL

Fixed error: Double value cannot be converted to Int because the result would be greater than Int.max in 32-bit devices

fixing a problem in safari webview and adding tabs to examples