Browser tests for shoping cart and checkout

Because of my confusion (see #15) I've implemented some black-box browser tests for the shopping cart and the checkout.

Changes included:

- Added a `development.cfg`
- Removed no-longer necessary source-checkout of collective.z3cform.wizard for Plone 4.3
- Removed `testing.py` (was not used) and added a new test setup.
- Use ftw.builder, ftw.testbrowser and page objects.
- Black-box browser tests for shopping cart.
- Black-box browser tests for checkout.
- Some HTML markup improvements (e.g. new classes for selecting elements in tests / page objects).

@lukasgraf could you take a look at this one? I'd also be interested in your opinion about #15 :wink: