chore(master): backfill missing copyright years

[tiborsimko]

Update source file copyright headers and top-level LICENSE files
to include the years in which each file was modified according to
git history, without following renames.

Closes reanahub/reana#973

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.20%. Comparing base (ee4735b) to head (faf1f80).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #183   +/-   ##
=======================================
  Coverage   87.20%   87.20%           
=======================================
  Files          42       42           
  Lines        3821     3821           
=======================================
  Hits         3332     3332           
  Misses        387      387           
  Partials      102      102           

Files with missing lines	Coverage Δ
cmd/close.go	95.74% <ø> (ø)
cmd/delete.go	94.11% <ø> (ø)
cmd/diff.go	86.66% <ø> (ø)
cmd/download.go	64.70% <ø> (ø)
cmd/du.go	94.80% <ø> (ø)
cmd/list.go	96.53% <ø> (ø)
cmd/logs.go	94.08% <ø> (ø)
cmd/ls.go	95.62% <ø> (ø)
cmd/mv.go	95.74% <ø> (ø)
cmd/open.go	95.00% <ø> (ø)
... and 25 more

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