Refactor: Hello: Make session a real citizen

Orient everything around separating
profile data from the session data,
which contains the logged-in patron
and the contributions he or she has
made.

Now we can move forward with the
notion of session data.
Refactor: Contribute: Use session data

Put the 'activeContribution' stuff into
the session data. Refactor the Contribute
page to bind to the session upon load,
which removes a bit of the crazy that was
being created.