Previously, DynamicArrayHandle and DynamicCellSet had slightly different
interfaces to their CastTo feature. It was a bit confusing and not all
that easy to use.

This change simplifies and unifies them by making each class have a single
CopyTo method that takes a reference to a cast object (an ArrayHandle or
CellSet, respectively) and fills that object with the data contained if
the cast is successfull. This interface gets around having to declare
strange types.

Each object also has a Cast method that has to have a template parameter
specified and returns a reference of that type (if possible).

In addition, the old behavior is preserved for DynamicArrayHandle (but
not DynamicCellSet). To avoid confusion, the name of that cast method is
CastToTypeStorage. However, the method was chaned to not take parameters
to make it consistent with the other Cast method.

Also, the IsType methods have been modified to reflect changes in
cast/copy. IsType now no longer takes arguments. However, an alternate
IsSameType does the same thing but does take an argument.