Update copyright header dates to 2020 (GSA 9)

[swaterkamp]

Checklist:

• [N/A] Tests
• CHANGELOG Entry

[codecov]

Codecov Report

Merging #2020 into gsa-9.0 will increase coverage by <.01%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##           gsa-9.0    #2020      +/-   ##
===========================================
+ Coverage    50.13%   50.13%   +<.01%     
===========================================
  Files         1067     1067              
  Lines        25016    25010       -6     
  Branches      7096     7065      -31     
===========================================
- Hits         12541    12540       -1     
+ Misses       11337    11333       -4     
+ Partials      1138     1137       -1

Impacted Files	Coverage Δ
gsa/src/stories/filefield.js	0% <ø> (ø)	⬆️
gsa/src/gmp/models/settings.js	100% <ø> (ø)	⬆️
gsa/src/stories/multiselect.js	0% <ø> (ø)	⬆️
gsa/src/gmp/cancel.js	100% <ø> (ø)	⬆️
gsa/src/gmp/parser.js	99.15% <ø> (ø)	⬆️
gsa/src/gmp/commands/testing.js	100% <ø> (ø)	⬆️
gsa/src/gmp/commands/users.js	33.33% <ø> (ø)	⬆️
gsa/src/gmp/commands/ovaldefs.js	53.84% <ø> (ø)	⬆️
gsa/src/gmp/models/scanconfig.js	98.57% <ø> (ø)	⬆️
gsa/src/stories/footnote.js	0% <ø> (ø)	⬆️
... and 176 more

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[bjoernricks]

Note sure if this will create conflicts during merging gsa 8

[swaterkamp]

There were other conflicts hard to find between almost 1500 changed files, that's why I made an extra PR for this, hoping git will be intelligent. Let's hope for the best ;)