Add dockerfile and shellcheck linters, refactor hack dir

[mszostok]

Description

Changes proposed in this pull request:

• Add dockerfile and shellcheck linters
• refactor hack dir
• refactor golangci-lint

[codecov]

Codecov Report

Merging #45 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #45   +/-   ##
=======================================
  Coverage   24.76%   24.76%           
=======================================
  Files          10       10           
  Lines         323      323           
=======================================
  Hits           80       80           
  Misses        239      239           
  Partials        4        4           

Impacted Files	Coverage Δ
internal/check/duplicated_pattern.go	78.57% <ø> (ø)
internal/check/file_exists.go	77.27% <ø> (ø)
internal/check/not_owned_file.go	0.00% <ø> (ø)
internal/check/valid_owner.go	0.00% <ø> (ø)
internal/ctxutil/check.go	100.00% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 32b0e86...95f4d05. Read the comment docs.