Java CommandHeader builder methods now all return CommandHeaders

[emgre]

Fix #417

[codecov]

Codecov Report

Merging #440 (5f41cc9) into develop (e8b1de4) will increase coverage by 0.04%.
The diff coverage is n/a.

❗ Current head 5f41cc9 differs from pull request most recent head 0140375. Consider uploading reports for the commit 0140375 to get more accurate results

@@             Coverage Diff             @@
##           develop     #440      +/-   ##
===========================================
+ Coverage    51.36%   51.41%   +0.04%     
===========================================
  Files          423      423              
  Lines        13444    13444              
===========================================
+ Hits          6906     6912       +6     
+ Misses        6538     6532       -6     

Impacted Files	Coverage Δ
cpp/lib/src/link/LinkFrame.cpp	95.06% <0.00%> (-1.24%)	⬇️
cpp/lib/src/app/parsing/CountIndexParser.cpp	59.74% <0.00%> (-0.65%)	⬇️
cpp/lib/src/gen/GroupVariation.cpp	31.72% <0.00%> (+0.24%)	⬆️
cpp/lib/src/link/LinkLayerParser.cpp	96.21% <0.00%> (+0.75%)	⬆️
cpp/lib/src/app/GroupVariationRecord.cpp	86.66% <0.00%> (+2.22%)	⬆️
cpp/lib/src/outstation/event/ClazzCount.h	100.00% <0.00%> (+5.45%)	⬆️

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