Consistent reference to content hash in data module

[ryanchristo]

Summary

When anchoring and attesting to data, the messages require Hash and Hashes as an input. When registering data to a resolver, the message requires Data. Each field represents one or more content hashes. A content hash also includes a Hash field. We should use consistent and more descriptive field names.

Problem Definition

Inconsistent use of field names in the data module when referring to a content hash.

Proposal

Update hash to content_hash, hashes to content_hashes, and data to content_hashes.

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