Cleanup and alphabetize plugin headers

[ahcorde]

🦟 Bug fix

Summary

This is part of the effort to move some of the plugin living in ign-gazebo to ign-gui. Refer to this issue #835

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge

[codecov]

Codecov Report

Merging #838 (235ff70) into ign-gazebo3 (65e8b04) will increase coverage by 0.04%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           ign-gazebo3     #838      +/-   ##
===============================================
+ Coverage        77.93%   77.98%   +0.04%     
===============================================
  Files              216      216              
  Lines            12131    12131              
===============================================
+ Hits              9454     9460       +6     
+ Misses            2677     2671       -6     

Impacted Files	Coverage Δ
src/gui/plugins/shapes/Shapes.cc	31.25% <ø> (ø)
.../gui/plugins/transform_control/TransformControl.cc	19.14% <ø> (ø)
src/SimulationRunner.cc	94.42% <0.00%> (+1.07%)	⬆️

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[mjcarroll]

LGTM. Assuming everything remaining are flaky tests?