replaced ViewingCart/ViewingAccount booleans and CheckoutStep int with a
single 'page' type and a SwitchPage() method, this is just almost
copying the reference implementation (terminalDotShop)'s routing
pattern. Adds inCartFlow(), chechoutStep(), and buildPageContent()
helpers to clean up those huge if/else chains in views, footer, header,
and breadcrumds. code is looking a lot better now!
