Implement new amendment majority semantics :

This implements the tracking of when an amendment achieved a majority
in the ledger, ensuring that there's always network-wide agreement
on which amendments have achieved a majority and how long they've
held it.

* New fields
* Change transactor changes
* AmendmentTable API and implementation changes
* Update amendment enabled status on validated ledgers
* Reinstate support for ledger sequence in fee transactions

src/ripple/app/main/DBInit.cpp

@@ -254,12 +254,6 @@ const char* WalletDBInit[] =
         PRIMARY KEY (Validator,Entry)                   \
     );",
 
-    "CREATE TABLE IF NOT EXISTS Features (              \
-        Hash            CHARACTER(64) PRIMARY KEY,      \
-        FirstMajority   BIGINT UNSIGNED,                \
-        LastMajority    BIGINT UNSIGNED                 \
-    );",
-
     "END TRANSACTION;"
 };