[#349] Remove the usage of mixin from Indigo CLI's generated boilerplate

Description

Problem: Since indigo CLI calls stack behind the scene, the usage of mixin in indigo CLI causes a lot of issue due the fact that stack does not work well with mixin currently.

Solution: Remove the usage of mixin from the generated boilerplate and use universum instead.

Related issue(s)

Resolves part of #349 (closed)

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