Resolve "Handle SBML render:fill in compartments"

Closes #1254 (closed)

changed milestone to %v15.1.0~beta.0

added enhancement SBML labels

added 3 commits

• 4f2a0738 - unused supres warnings removed
• 0e633ee9 - font color is properly encoded and compartments properly handle fill color
• c5e5fba8 - fill color is exported to sbml

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added 3 commits

• c5e5fba8...a4087e49 - 2 commits from branch master
• 2beedcd6 - Merge remote-tracking branch 'origin/master' into 1254-handle-sbml-render-fill-in-compartments

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unmarked as a Work In Progress

enabled an automatic merge when the pipeline for 2beedcd6 succeeds

mentioned in commit 83e90035

merged