Fix GUI warnings and add missing GUI update in example 2

[wahln]

#856 identifies a missing GUI update in example 2, which was added in this PR.

Additionally, two bugs concerning a missing conf3D flag as well as a mistake in the pln/stf comparison were fixed.

[codecov]

Codecov Report

Attention: Patch coverage is 41.17647% with 10 lines in your changes missing coverage. Please review.

Project coverage is 53.03%. Comparing base (e9411f8) to head (d3368b0).
Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
matRad/gui/widgets/matRad_WorkflowWidget.m	0.00%	9 Missing ⚠️
matRad/util/matRad_comparePlnStf.m	87.50%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #857   +/-   ##
=======================================
  Coverage   53.02%   53.03%           
=======================================
  Files         307      307           
  Lines       19787    19794    +7     
=======================================
+ Hits        10493    10497    +4     
- Misses       9294     9297    +3     

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[github-actions]

Package	Line Rate	Health
coverage Package 1	53%	➖
Summary	53% (10490 / 19794)	➖

[github-actions]

Test Results

  3 files  ±0    3 suites  ±0   42m 18s ⏱️ -2s
287 tests ±0  287 ✅ ±0  0 💤 ±0  0 ❌ ±0 
957 runs  ±0  952 ✅ ±0  5 💤 ±0  0 ❌ ±0 

Results for commit d3368b0. ± Comparison against base commit e9411f8.