The Wallet object used to have a guarenteed lifetime longer than the App
singleton, but then we started allowing people to delete their wallet
(argh!).
Also "external" modules, especially living outside of the main tree,
would be much more stable if they can avoid using raw pointers for core
concepts like the Wallet.
This fixes some cornercases and makes the test
a) properly data-driven (don't use 'today').
b) much more extensive.
This also removes some duplicate code and fixes some bugs in the actual
model it tests.