Authentication Changes

Ty, these are the latest changes - I believe they incorporate all the changes you made to your code from yesterday. I didn't know how to pull your changes from yesterday's session and merge them into my own code, so I had to manually do that ... hopefully I've captured everything.

Two major changes:

* User can only see their own tips (when signed in) in the "Create Tip" page
* Users can only see site content if they are signed in (authentication)