iOS Fixes for React Native 0.43

#22 Fix compile on iOS

SDK Updates, Typos

#8 - Update to React Native 0.40
#21 - iOS Typos
#11 - Update Twilio SDKs (0.17.1/0.12.1)

Bug Fixes + Message Attributes

Fixed several Android bugs and added support for adding message attributes on send.

• java.lang.ClassCastException: com.twilio.chat.ChannelDescriptor cannot be cast to com.twilio.chat.Channel
• [Android] int com.twilio.chat.ChatClient$SynchronizationStrategy.getValue() on null object reference
• [programmable-chat][android] TwilioAccessManager.registerClient() is undefined
• Send message with attributes

Thank you for your continued support and patience while we get this package updated.

Initial Release

This is basically the release of the programable-chat branch from react-native-twilio-ip-messaging.

Please review the Migration docs if you are upgrading an existing project.