Periodic verification tools

A precursor to payments, we should have some methods and commands for a storage client to check a catalog file of all data known to be stored on a peer (a sort of storage channel). Catalogs can store padding, chunks, and other variables, especially for lookup and indexing (clientside search).

Start by locating the storage client and its command entry points, then trace how catalog files represent padding, chunks, lookup, and indexing. No files or tests are named in the issue. Done should mean there is a defined, tested design for periodic verification methods and commands that check all data known to be stored on a peer.

Written by the indexing model from the issue text.