Change fee escalation algorithms (RIPD-1177):

* Minimum factor 256*500, don't multiply by base fee
* Change autofill fee behavior to pay the open ledger fee.
** Experimental options: x-assume-tx - assume <int> more transactions in
   the open queue when computing escalated fee, x-queue-okay - if true
   and escalated fee is over limit, try with load fee.
* Port of 75af4ed.

src/ripple/app/misc/NetworkOPs.cpp

@@ -2093,7 +2093,7 @@ Json::Value NetworkOPsImp::getServerInfo (bool human, bool admin)
         info[jss::load] = m_job_queue.getJson ();
 
     auto const escalationMetrics = app_.getTxQ().getMetrics(
-        app_, *app_.openLedger().current());
+        app_.config(), *app_.openLedger().current());
     if (!human)
     {
         info[jss::load_base] = app_.getFeeTrack ().getLoadBase ();