atto photon refactor

[fedekunze]

Description

• add utility functions for atto photon
• add an additional coin-denom flag to testnet command in order to remove testnet command on Aragon Chain

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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/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #503 into development will decrease coverage by 0.08%.
The diff coverage is 27.27%.

@@               Coverage Diff               @@
##           development     #503      +/-   ##
===============================================
- Coverage        71.81%   71.73%   -0.09%     
===============================================
  Files               40       41       +1     
  Lines             2679     2685       +6     
===============================================
+ Hits              1924     1926       +2     
- Misses             614      618       +4     
  Partials           141      141              

Impacted Files	Coverage Δ
types/account.go	62.16% <0.00%> (ø)
types/coin.go	33.33% <33.33%> (ø)
x/evm/types/params.go	100.00% <100.00%> (ø)

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