Make in_column the first argument in every transform

[alex-hse-repository]

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Before submitting (must do checklist)

• Did you read the contribution guide?
• Did you update the docs? We use Numpy format for all the methods and classes.
• Did you write any new necessary tests?
• Did you update the CHANGELOG?

Type of Change

• Examples / docs / tutorials / contributors update
• Bug fix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves an existing feature)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Proposed Changes

Make in_column the first argument in every transform

Related Issue

Closing issues

closes #215

[codecov-commenter]

Codecov Report

Merging #247 (7367be5) into master (3853ec3) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #247   +/-   ##
=======================================
  Coverage   86.43%   86.43%           
=======================================
  Files          89       89           
  Lines        4240     4240           
=======================================
  Hits         3665     3665           
  Misses        575      575           

Impacted Files	Coverage Δ
etna/transforms/scalers.py	100.00% <ø> (ø)
etna/transforms/sklearn.py	95.83% <ø> (ø)
etna/transforms/add_constant.py	100.00% <100.00%> (ø)
etna/transforms/lags.py	100.00% <100.00%> (ø)
etna/transforms/statistics.py	98.80% <100.00%> (ø)

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[Mr-Geekman]

Should we delete this space?

[alex-hse-repository]

No we should't)