added clearHistory webview methods on Android, setContextMenu and clearFocus webview methods, added ContextMenuOptions class

Added 'toString()' method to various classes in order to have a better output instead of simply 'Instance of ...', updated getOptions() method

added onPageCommitVisible event, updated dart code for new events and methods, updated docs, fix #367

Updated Android context menu workaround, updated iOS onCreateContextMenu event, Added Android keyboard workaround to hide the keyboard when clicking other HTML elements

expiresDate option (#338)

added HeadlessInAppWebView class, added close, addMenuItem and addMenuItems methods to ChromeSafariBrowser, added ChromeSafariBrowserMenuItem class, fixed InAppWebView.channel null exception on android, fix #305, fix #245, fix #299

fix scrollbar on iOS always show if not disable scroll

Fix crash when `prompt` was called on Android Q.

Fix crash on nil/invalid URL (iOS)

Fix config options for Android release builds

>  onLongPressHitTestResult event, updated test cases, fixed Promise polyfill, fixed android options

Using reflection was not a good idea because when the Android App is
compiled for release mode, some code optimizations are executed. The
fields of the configuration classes were then renamed and the mapping
via reflections did not work again. Now everything has an explicit
mapping form the untyped HashMap to the class fields and vice versa.

code refactoring, added InAppBrowserManager and ChromeSafariBrowserManager classes on native code, updated webview options class names

updated ChromeSafariBrowser class, Renamed Chrome Custom Tab addShareButton option to addDefaultShareMenuItem, Renamed ChromeSafariBrowser onLoaded to onCompletedInitialLoad, Renamed all iOS and Android webview options class, fix #229, Added packageName and keepAliveEnabled ChromeCustomTab options for Android