Add display conditions to Fields.
Change Fields attribute "value" to "default value", and remove errors, these are now provided via the renderer.
Update programmatic form definitions to use modified functionality.
Refactor trolley-details to a component and include in checkout page.  Remove checkout-form component (call forms module directly from checkout page).
Add processors to checkout form builder.
Fix typo.
Text change.
Prevent access to checkout with empty trolley (bounce to trolley details page).
Prevent access to checkout with non-logged-in user (bounce to login page).
Changes to default text configuration items.
View script code formatting consistency.
Improve behaviour when generating a link with a return URL that itself already contains a return URL.
WIP login / sign-up / proceed-as-guest selector.