Refactor View classes:

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.

src/ripple/app/tx/impl/SetAccount.cpp

@@ -24,6 +24,7 @@
 #include <ripple/protocol/Indexes.h>
 #include <ripple/protocol/Quality.h>
 #include <ripple/protocol/TxFlags.h>
+#include <ripple/ledger/View.h>
 
 namespace ripple {