Following skeletal end to end flow work, this submit
takes the next steps for Endorser/Committer
  . converts chaincode and endorser to ledgernext
  . removes consensus package
  . chaincode unit tests use ledgernext
  . panics if ledger.GetLedger is called so we
    can catch codepaths that still use that. These
    are mainly core/api and core/peer
  . removes unit tests from core/api and core/ledger
    (to avoid GetLedger calls there)
  . created a minimal core/peernext. core/peer is
    still there for comparison but is not used

Change-Id: I2627e0000e960e1aa66d27ff5ec60a38c4bb7eea
Signed-off-by: Srinivasan Muralidharan <muralisr@us.ibm.com>