Refactor consensus for simulation (RIPD-1011):

This is a substantial refactor of the consensus code and also introduces
a basic consensus simulation and testing framework.  The new generic/templated
version is in src/ripple/consensus and documents the current type requirements.
The version adapted for the RCL is in src/ripple/app/consensus.  The testing
framework is in src/test/csf.

Minor behavioral changes/fixes include:
* Adjust close time offset even when not validating.
* Remove spurious proposing_ = false call at end of handleLCL.
* Remove unused functionality provided by checkLastValidation.
* Separate open and converge time
* Don't send a bow out if we're not proposing
* Prevent consensus stopping if NetworkOPs switches to disconnect mode while
  consensus accepts a ledger
* Prevent a corner case in which Consensus::gotTxSet or Consensus::peerProposal
  has the potential to update internal state while an dispatched accept job is
  running.
* Distinguish external and internal calls to startNewRound.  Only external
  calls can reset the proposing_ state of consensus

src/test/jtx/impl/Env.cpp

@@ -30,7 +30,7 @@
 #include <test/jtx/utility.h>
 #include <test/jtx/JSONRPCClient.h>
 #include <ripple/app/ledger/LedgerMaster.h>
-#include <ripple/app/ledger/LedgerTiming.h>
+#include <ripple/consensus/LedgerTiming.h>
 #include <ripple/app/misc/NetworkOPs.h>
 #include <ripple/app/misc/TxQ.h>
 #include <ripple/basics/contract.h>