[REFACTOR] Formula/creator

[victor-schumacher]

- What I did
A general refactor at creator.go and and templates.

- How I did it

Changing create functions to be more generic;
Segregated the creation of packge.json, so in future, it can be used by another languages like typescript;
Removed some unused string operations;
Removed the "Template" before each tpl_lang.go variable, since it's inside a tpl file.

- How to verify it
It's a refactor pull request, so you can just make sure everything is ok.

- Description for the changelog
general refactor at creator.go and and templates.

[codecov-commenter]

Codecov Report

Merging #98 into master will decrease coverage by 1.13%.
The diff coverage is 96.55%.

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
- Coverage   44.34%   43.20%   -1.14%     
==========================================
  Files          56       56              
  Lines        2156     2104      -52     
==========================================
- Hits          956      909      -47     
+ Misses       1040     1035       -5     
  Partials      160      160              

Impacted Files	Coverage Δ
pkg/formula/creator.go	71.09% <96.55%> (-2.52%)	⬇️

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[victor-schumacher]

refactor pkg/formula/creator.go

[GuillaumeFalourd]

The correction of the functional-test that broke the circle-ci build has been implemented in this PR : #97