[Release][v.1.5] Load dependencies in one shot and mirror code refactoring

[francescofrontera]

Due to Coronavirus Lookdown, I did some optimization:

• avoid to read JSON for all task operation;
• use a custom Model for all information (Dependencies, Credentials, and Resolver);
• ensure referential transparency.

Stay healthy and have a beautiful day's guys!

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (develop@0b2e3cf). Click here to learn what that means.
The diff coverage is n/a.

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  Coverage           ?   52.63%           
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  Files              ?        5           
  Lines              ?       19           
  Branches           ?        0           
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  Hits               ?       10           
  Misses             ?        9           
  Partials           ?        0           

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