change photon to aphoton

[J-Thompson12]

Closes: https://github.com/ChainSafe/ethermint/issues/434

Description

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
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• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
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[codecov]

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  Files                  ?       38           
  Lines                  ?     2493           
  Branches               ?        0           
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  Hits                   ?     1745           
  Misses                 ?      617           
  Partials               ?      131           

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[fedekunze]

Thanks!

Can you add new doc under docs/basics/photon.md that says that the base denomination of Ethermint is the atto Photon to maintain parity Ethereum (and add the conversion formula from the issue). 🙏

[fedekunze]

here's a photon token image for the docs too: