https://jira.hyperledger.org/browse/FAB-1390



A few things changed according to FAB-1390 description and the latest NCAP
1. renamed RawLedger interface to OrdererLedger
2. added PeerLedger interface which keeps a bitmask to indicate invalid transactions as described in NCAP
3. changed ledger API description in Next-Ledger-Architecture-Proposal
4. refactored rawledger package to ordererledger in orderer directory

Please notice that with this change set, there'll be cases of inconsistent package names with import path.
This is a tradeoff to avoid stuttering path names
These cases are listed as below.

Package name, import path
(ordererledger, github.com/hyperledger/fabric/orderer/ledger)
(ramledger, github.com/hyperledger/fabric/orderer/ledger/ram)
(fileledger, github.com/hyperledger/fabric/orderer/ledger/file)

Change-Id: Ie9580678ee9012ff865d1dc507066f46e106f250
Signed-off-by: Xi Xue Jia <xixuejia@gmail.com>