feat(typing-indicator): use isTyping in MessageContainer to renderFooter
feat(typing-indicator): use isTyping in MessageContainer to renderFooter

-DRY footerprops
-if renderFooter is provided by the user then return their custom indicator
-otherwise return our own prepackaged indicator
-extraData should be an array not an object
-pass isTyping to extraData so that FlatList renders

FaridSafi/react-native-gifted-chat,FaridSafi/react-native-gifted-chat