add screenshot feature

[snoyer]

Screenshot interaction feature as per #1194. Draft PR mostly because I'm not sure how to go about the testing.

[codecov]

Codecov Report

Attention: Patch coverage is 97.61905% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 96.57%. Comparing base (f0a3730) to head (d20b440).
Report is 6 commits behind head on master.

Files	Patch %	Lines
application/F3DStarter.cxx	97.60%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1391      +/-   ##
==========================================
+ Coverage   96.55%   96.57%   +0.01%     
==========================================
  Files         103      103              
  Lines        7555     7679     +124     
==========================================
+ Hits         7295     7416     +121     
- Misses        260      263       +3     

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[mwestphal]

Needs a doc update

[mwestphal]

Small changes needed. Improving the doc would also be nice and help with the release notes :)

[mwestphal]

small changes needed