(Improvement) Add keccak identifier

[phahulin]

• What is it? (leave one option)

  • (Improvement) of existing functionality

• What was the root cause of the problem originally / what feature was missing? In light of integration with erc780 it would be convenient to get keccak hash of an address as seen by the PoPA contract, to check it in erc780 registry.

• How does this pull request solve it (in broad terms)? Add keccakIdentifier return value to userAddressInfo function

• Does it close any open issues?

• Quick checklist

  • [X] npm run lint shows no errors
  • [X] docs were updated where necessary OR they don't need to be updated
  • [X] tests were updated where necessary OR they don't need to be updated

• Additional information Merge after #95

[coveralls]

Pull Request Test Coverage Report for Build 301

• 0 of 0 (NaN%) changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 72.284%

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Totals
Change from base Build 299:	0.0%
Covered Lines:	799
Relevant Lines:	1057

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💛 - Coveralls

[phahulin]

@fvictorio also please take a look at this PR