Move up a layer to the HTTP. Also, start to remove ContextWrapper
stuff. We've done it differently for App Engine instead, and will do
it differently yet moving forward.
Also add blobserver.Receive and use it in most places, moving checksum
verification up a layer.
Bunch of other cleanup and TODO fixing too.
Much simpler and cleaner.
Change-Id: I12e56c5d4e53bfcf82bdd8fb0b6d57c248ff605c
Brad Fitzpatrick