CRM-15474 - Move js-based form alterations to php

I'm not totally happy with this because

a) Why do we even need special logic to hide the 'Pending from cart' option if cart is disabled? That option should be programatically disabled if cart is disabled.
b) The logic to hide the "Pending refund" status is not entirely sound, it gets hidden on initial load of the form but would show up if you edited the option list in a popup and saved (the dropdown would get refreshed from the api, which wouldn't respect the logic used on the form).

Oh well.