CBIDXT-64 Initial Implementation of MutationStreamReader

MutationStreamReader reads a MutationStream and stores the incoming mutations
in mutation queue. This is the only component writing to a mutation queue.

Change-Id: If047ff9f47d5ad1ace944c9726be181d685af240
Reviewed-on: http://review.couchbase.org/36465
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Tested-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>