The main motivation for the changes is to improve the efficiency
of AMR data structures by replacing the data set containers and meta
data representation with new data structures.

First, the meta data associated with the AMR data is moved from
vtkInformation to a new class vtkAMRInformation so that they do not
have to be deep copied. Related changes also include:

- Before, when the LOAD_REQUESTED_BLOCKS() key is not set, the reader
  would recompute AMR meta data based on the requested blocks.  This
  is no longer done: meta data always represents what is on file.
  The reason is to avoid the sensitive meta data computation that
  depends on connectivitiy of the requested blocks.

- Processor ranks are no longer stored in the meta data. Filters
  can easily generate them by using
  vtkAMRUtilities::DistributeProcessInformation

- There used to be two types of 1D indices used to reference blocks in
  an AMR: vtkOverlappingAMR::GetFlatIndex and
  vtkOverlappingAMR...