Added functionality for Google Calendar Manager to check online status

Why is this change necessary?
- Previously, when the user is offline, GoogleCalendarManager thinks that
  the authorization key is invalid, and prompts the user to generate a new
  key,   even if the key may actually still be valid.

How does it address the issue?
-  GoogleCalendarManager now calls the method "isUserOnline" to check for
   online status of the user. This method pings google's servers to
   determine connectivity with Google. If the ping fails, a false boolean
   variable is returned to the database.