Don't lard up InternalClient with extra middleware

One can argue that it makes sense for the client-facing proxy server
to have certain middlewares like gatekeeper in its pipeline, but that
is not desirable for InternalClient. In particular, it prevents you
from passing in sysmeta headers using InternalClient, and I found
myself wanting to do that earlier today.

Now InternalClient's proxy application gets exactly what's configured;
no more, no less. This will mean that the object expirer can read and
write sysmeta headers, but I think we can trust it to keep our
secrets.

Change-Id: I17b4a89c24e600754701ee1645b40406421fa6f3
fix gatekeeper response headers behavior

removes @wsgify decorator
changes code to a more traditional way of messing with response headers

Change-Id: I13ce7f98bae48eb0b990a64aa6f3d63ff8d13bf5
Closes-Bug: 1285392
Convert all old-style classes to new-style

This cleanup has been slowly happening for a while; let's finish it.

Change-Id: I1561e3540d524834e0cc5bc725ab80936eae1f0e
Merge "fix gatekeeper response headers behavior"
Merge "Don't lard up InternalClient with extra middleware"