Update distributed array protocol implementation

The Distributed Array Protocol has been changed since it was first implemented in DistArray.  See commit messages for each individual change that is made in this PR.  These are mostly simple naming changes, with the exceptions of:

1) removing the 'bc' dist type (and adding the 'block_size' keyword to 'c')
2) removing the 'bp' dist type
3) changing the 'dist_type' for no-distribution to 'n' (from None).