Add couch_notifier_enabled engine parameter

This allows us to disable couchdb notifications so that
we can run memcached with ep-engine and couchstore

Change-Id: I9a3c50443ff35b7a602803f229ea0b0b793b7125
UPR consumer add_stream command.

Change-Id: I40332293a9ae5df0c366297041b4d8d3fa871668
WIP

Change-Id: Iaae0acf005bb568b263b67f04b33ad9b74a9131e