Freedom Chat demo using GoogleTalk protocol

First version of chat demo using GoogleTalk protocol.  Demo functionality illustrates:
* Signing in to GoogleTalk using Oauth2 web flow.
* Displaying GoogleTalk buddy list.
* Chatting between other instances of chatdemo and other GoogleTalk clients (e.g. gmail).

Tested using chats between uproxy.eva and harryuproxy accounts, with uproxy.eva using the chatdemo client and harryuproxy using both chatdemo and GoogleTalk within the gmail website.