- eliminate redundant size_ accounting

- drop extra 'Container' template parameter and replace functionality
  with more flexible pack/unpack methods.
  There is also a pack() method that handles indirect lists of lists
  that can be used, for example, to pack a patch slice of faces.

  Drop the 'operator()' method in favour of unpack to expose and properly
  document the conversion. Should revisit the corresponding code in
  some places for optimization potential.

- align some method names with globalIndex:
  totalSize(), maxSize() etc