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.