Bubble results from WePay / WePayResource as Futures.

From now on, these files don't require a future to materialize before
doing their work. The respective API resources still need to be updated,
but this is the first step to the point where client code is responsible
for managing the concurrency of their WePay requests.
App resource compiles with futures.
Implement unwrapBoxOfFuture helper.
Account resource compiling.
Checkout resource compiling.
CreditCard resource is compiling.
Show deprecation and feature warnings during compile.
Tests compile.
Nuke a deprecation warning.