Detect whether timezone needs to be changed

The goal of this patch is to remove the "percentage" setting from autotimezone, and to instead have the module detect whether timezone data needs to be sent.

The javascript now detects whether the user's timezone needs to be updated. Now the timezone data is only sent if the timezone offset detected by the javascript does not match the user's timezone setting in Drupal. If the session variable for anonymous users is turned on, the effect is the same -- it is only updated if the javascript detects a different timezone setting.

Furthermore, if the session variable for anonymous users is turned off, and the user is anonymous, the javascript isn't even added to the page.