v0.1.0 of erxes_flutter_sdk

Flutter plugin for the Erxes messenger, wrapping the native iOS and Android Erxes SDKs. Changelog excerpt: - Initial release. - ErxesMessengerAPI: configure, setUser, clearUser, showMessenger, hideMessenger, showLauncher, hideLauncher, plus onActionand onReadystreams. - Android: wraps io.github.munkhorgilb:messenger-sdk(chat mode). - iOS: wraps MessengerSDKfrom erxes-ios-sdkvia Swift Package Manager (chat + classic launcher).