Redesign StorageBasic to allow modification of user provided memory.

The driving desire for this change was to make vtk-m ArrayHandle behave more like the standard vector. The canonical example of what we want to support is:

std::vector<vtkm::Id> values;
values.resize(100);
vtkm::cont::ArrayHandle<vtkm::Id> array = vtkm::cont::make_ArrayHandle(values);
vtkm::cont::DeviceAdapterAlgorithm<DeviceAdapter>::Sort(array);

And with-out the ability to modify user provided memory, this was impossible.