Go through db pinning after successful shared secret auth (bug 951946)

We weren't pinning properly everytime (when you first go through the
db pinning middleware, it's too early, you aren't authenticated yet,
so we don't pin you), this might explain weird bugs after actions,
such as collection re-ordering issues...
Revert "Revert "Remove password from IARC form"" (bug 952288)

This reverts commit 7bb5f2a86bbe29341776d55cc971f259ed2062be.

IARC now ignoring password.
add Cache-Control/Expires/ETags/Last-Modified headers to Marketplace (bug 946845)
remove old tastypie test helper: `assertImmediate`