ROL-1999 Addition of #showAnalyticsTrackingCode() macro to include tracking keys into HTML header section; addition of this macro to default templates provided by Roller; update to user's and template guide explaining how this works.

git-svn-id: https://svn.apache.org/repos/asf/roller/trunk@1598868 13f79535-47bb-0310-9956-ffa450edef68