Add new Google Calendar functionality

Implemented package org.springframework.social.google.api.calendar and org.springframework.social.google.api.calendar.impl, and offline autotests.
Also see spring-social-google-example updates for manual online testing.

Within the existing code I've moved encode() up a level to QueryBuilderImpl so it's available to all builders.
Also includes a fix for issue #62 - wrong time format in QueryBuilderImpl.
In AbstractGoogleApiOperations constructor I add an error handler to the restTemplate to log the response body, since Google sends back JSON that explains the error, for instance lack of permission.