push-guestbook: Added retry logic to the client.

Formerly, if there was an error in the client's connection
to the server, it would just quietly bomb out and fail to continue
initializing its state.  Now it will retry every 5 seconds.  Note
that if getChannelId fails it will still just not function correctly.
Merge pull request #128 from mrdewitt/push-guestbook-retry

push-guestbook: Added retry logic to the client.