allow custom csp header
allow custom csp header

PR: #514
PR-URL: https://github.com/apache/couchdb-fauxton/pull/514
Reviewed-By: Benjamin Keen <3e66e8841d2ec9e6067d8d313dccb27f5f6bb2e9@gmail.com>

popojargo/couchdb-fauxton,popojargo/couchdb-fauxton,michellephung/couchdb-fauxton,michellephung/couchdb-fauxton,popojargo/couchdb-fauxton,garrensmith/couchdb-fauxton,garrensmith/couchdb-fauxton,robertkowalski/couchdb-fauxton,cloudant/couchdb-fauxton,apache/couchdb-fauxton,robertkowalski/couchdb-fauxton,apache/couchdb-fauxton,popojargo/couchdb-fauxton,michellephung/couchdb-fauxton,cloudant/couchdb-fauxton,benkeen/couchdb-fauxton,apache/couchdb-fauxton,garrensmith/couchdb-fauxton,robertkowalski/couchdb-fauxton,robertkowalski/couchdb-fauxton,cloudant/couchdb-fauxton,cloudant/couchdb-fauxton,michellephung/couchdb-fauxton,benkeen/couchdb-fauxton,apache/couchdb-fauxton,benkeen/couchdb-fauxton,michellephung/couchdb-fauxton,garrensmith/couchdb-fauxton