This change set implements a base communication layer for
the raft orderer, but it can actually be used for any
consensus protocol that has:
- A specified number of members at any given point in time
- uses TLS pinning for identification
- Represents members as integers

The communication has 3 basic capabilities:

1) Obtain a remote context given a destination node ID and a channel
2) Configure the communication on the context of a given channel
3) Get notified of Step() and Submit() messages from other remote nodes

Change-Id: I87f193b7723f95f359cc4071e28b362be703ab74
Signed-off-by: yacovm <yacovm@il.ibm.com>