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
The View hierarchy of classes is reorganized to include new
classes with member functions moved and renamed, to solve
defects in the original design:
OpenView accumulates raw state and tx changes and
can be applied to the base. ApplyView accumulates changes
for a single transaction, including metadata, and can be
applied to an OpenView. The Sandbox allows changes with
the option to apply or throw them out. The PaymentSandbox
provides a sandbox with account credit deferral.
Call sites are changed to use the class appropriate for
the task.
