(Refactor) Refactor of prepare_reg_tx route

[garatortiz]

• What is it? (leave one option)

  • (Refactor) of existing code (no functionality change)

• What was the root cause of the problem originally / what feature was missing? The original code of the prepare_reg_tx was not very testable and maintainable.

• How does this pull request solve it (in broad terms)? Simplify code in order to make it more readable and testable by mainly extracting and refactoring functions.

• Does it close any open issues? Closes #19

• Quick checklist

  • [X] eslint shows no errors

    cd web-dapp
    eslint .

  • [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 This PR also adds the prepareRegTx controller tests

[coveralls]

Pull Request Test Coverage Report for Build 112

• 54 of 93 (58.06%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+7.02%) to 30.849%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
web-dapp/server-lib/post_api.js	0	5	0.0%
web-dapp/controllers/prepareRegTx.js	54	64	84.38%
web-dapp/routes/prepare_reg_tx.js	0	24	0.0%
<!--	Total:	54	93	58.06%	-->

Files with Coverage Reduction	New Missed Lines	%
web-dapp/routes/prepare_reg_tx.js	1	0.0%
<!--	Total:	1		-->

Totals
Change from base Build 102:	7.02%
Covered Lines:	325
Relevant Lines:	997

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💛 - Coveralls

[phahulin]

hurray, travis passed at last:)