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/protocol/STObject.h

@@ -99,6 +99,10 @@ public:
     STObject (const SOTemplate & type, SField const& name);
     STObject (const SOTemplate & type, SerialIter & sit, SField const& name);
     STObject (SerialIter& sit, SField const& name);
+    STObject (SerialIter&& sit, SField const& name)
+        : STObject(sit, name)
+    {
+    }
     STObject& operator= (STObject const&) = default;
     STObject& operator= (STObject&& other);